EPA-560/6-78-010
AN EVALUATION
OF THE ORGANOCHROMIUM
CONTENT OF SEWAGE SLUDGE
JANUARY 1979
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF TOXIC SUBSTANCES
I, D.C. 20460
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AN EVALUATION OF THE ORGANOCHROMIUM CONTENT
OF SEWAGE SLUDGE
by
Paul L. Sherman
Joseph J. Brooks
Leroy Metealfe
Thomas J. Hoogheem
Monsanto Research Corporation
Dayton Laboratory
Dayton, Ohio 45407
EPA-560/6-78-010
Contract 68-01-1980
Project Officer
John H. Smith
January 1979
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF TOXIC SUBSTANCES
WASHINGTON, D.C. 20460
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EPA REVIEW NOTICE
This report has been reviewed by the Office of Toxic Substances,
U.S. Environmental Protection Agency, and approved for publi-
cation. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Pro-
tection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
11
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ABSTRACT
The organochromium content of sewage sludge was evaluated during
this study. Sewage sludges containing chromium were obtained.
These sludges were analyzed to determine total chromium and then
fractionated to obtain four chromium fractions. The fractions
represented soluble chromium, cationic chromium which was dilute
acid soluble, and alkali soluble and insoluble fractions. The
two later fractions represent the chromium which is associated
with humus and humin respectively-
Mixtures of the sludges were analyzed for total and fractionated
chromium. These mixtures were then subjected to aerobic and
anaerobic digestion for 30 days. After the 30 day period the
sludge mixtures were reanalyzed.
Good mass balances were obtained for both the distribution of
chromium among fractions compared with total chromium analyses
and between before and after digestion samples. Data also was
collected from the four fractions described earlier (for
twenty-two other elements). These data were collected for
sludge mixtures both before and after digestion studies. Com-
parisons were made of the distribution of the various elements.
111
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CONTENTS
Abstract iii
Figures
Tables
1. Summary 1
2. Introduction 3
3. Background 5
3.1 Proposed Approach 7
3.2 Description of the Sewage Treatment Plant. ... 8
4. Experimental 10
4.1 Sampling Treatment Plant 10
4.2 Aerobic and Anaerobic Digestion 12
4.2.1 Anaerobic Digestion 12
4.2.2 Aerobic Digestion 14
4.3 Fractionation and Extraction 16
4.4 Analysis 19
5. Results and Discussion 22
5.1 Sewage Treatment Plant Samples 22
5.2 Total Chromium Analyses 24
5.3 Sewage Sludge Fractionation 25
5.4 Results for Other Elements 28
References 33
v
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FIGURES
Number Page
1 Aerial view of Guthrie Road sewage treatment
plant with sampling locations 11
2 Anaerobic digestion experimental apparatus 13
3 Aerobic digestion experimental apparatus 15
4 Separation scheme for chromium in sewage sludge. . . 18
5 Atomic absorption chromatogram of chromium
in a mixture of organochromium compounds 21
6 Schematic of sampling locations at the
sewage treatment plant 23
VI
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TABLES
Number page
1 Removal of Chromium by Various Chemical
Treatment Processes (2) 5
2 Atomic Absorption Conditions for Chromium Analyses . 19
3 High Performance Liquid Chromatography Conditions
for Orgahochromium Analysis 20
4 Distribution of Chromium Throughout the Sewage
Treatment Plant 24
5 Total Chromium Analysis Results for Sewage Sludges . 25
6 Comparison of Total Chromium Values, Theoretical
and Actual, of Sludge Mixtures 25
7 Chromium Concentration in the Liquid Portion of
Sewage Sludge Mixtures 26
8 Comparison of Atomic Absorption and Inductively
Coupled Argon Plasma Analysis of Chromium in
Sewage Sludge Fractions 27
9 Elements Analyzed in Sewage Sludge 29
lOa Concentration of Selected Elements in Fractions of
Sewage Sludge Samples 30
lOb Concentration of Selected Elements in Fractions of
Sewage Sludge Samples 31
11 Digestion Effects on the Percentage of Selected
Elements in the 0.5N NaOH Extractable Fraction
of Sewage Sludge 32
VI1
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SECTION 1
SUMMARY
The objective of this study was to evaluate the organochromium
content of sewage sludge. There are three important questions
to be answered in order to better understand the fate of chromi-
ium in sewage treatment plants: First, is there formation and
subsequent loss of volatile organochromium compounds resulting
in transferral of chromium from the treatment plant to the
surrounding environment during aeration or digestion processes?
Second, is the chromium being effectively removed from the
aqueous portion of the sewage during treatment? Third, what is
the molecular form of the chromium which is associated with the
sludge from the treatment processes? The answers to questions
one and two were determined during the study. The volatile
organochromium compounds, if present, would have been collected
on a porous polymer resin during simulated aerobic and anaerobic
digestion studies. Distribution of chromium between aqueous and
solid fractions at various points throughout the sewage treatment
plant was determined as a partial answer to question two. In
response to question three, experiments were devised to determine
the distribution of chromium in sludges among soluble, cationic
(acid soluble), alkali soluble and nonalkali soluble fractions.
This fractionation was performed before and after simulated
aerobic and anaerobic digestions.
While the mass balances obtained for the study were good, an
original objective of obtaining high performance liquid chroma-
tography-atomic absorption (HPLC-AA) information concerning
polarity and molecular weight distribution for the organochromium
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compounds was not met because it was not possible to raise the
chromium content of the aqueous layer by concentration techniques,
In the four fractions listed earlier, information was also ob-
tained with regard to the distribution of 22 other elements.
All results were obtained for both before and after samples from
both aerobic and anaerobic digested sludges.
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SECTION 2
INTRODUCTION
The evaluation of the organochromium content of sewage sludge
was conducted by Monsanto Research Corporation (MRC) in response
to Research Request No. 3 of Contract No. 68-01-1980 with the
United States Environmental Protection Agency's Office of Toxic
Substances (EPA/OTS). During Research Request No. 1 of the same
contract MRC had sampled the sewage sludge at the City of Dayton
Guthrie Road sewage treament plant (1). The study had deter-
mined the total chromium and the chromium in the diethyl ether
extractable portion of the sludge. The diethyl ether extract-
able portion was found to contain only 1% of the total chromium
in the sludge. In order to more fully understand the fate of
chromium during sewage treatment the study described in this
report was undertaken.
There are three important questions to be answered in order to
better understand the fate of chromium in sewage treatment plants:
First, is there formation and subsequent loss of volatile organo-
chromium compounds resulting in transferral of chromium from the
treatment plant to the surrounding environment during aeration
or digestion processes? Second, is the chromium being effect-
ively removed from the aqueous portion of the sewage during
treatment? Third, what is the molecular form of the chromium
which is associated with the sludge from the treatment proces-
ses? The answers to questions one and two were determined
during the study. The volatile organochromium compounds, if
present, would have been collected on a porous polymer resin
during simulated aerobic and anaerobic digestion studies. Dis-
tribution of chromium between aqueous and solid fractions at
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various points throughout the sewage treatment plant was deter-
mined as a partial answer to question two. In response to
question three, experiments were devised to determine the dis-
tribution of chromium in sludges among soluble, cationic (acid
soluble), alkali soluble and nonalkali soluble fractions. This
fractionation was performed before and after simulated aerobic
and anaerobic digestions. The results from each of these
studes are detailed in the following background, experimental,
and results and discussion sections.
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SECTION 3
BACKGROUND
In typical municipal sewage treatment facilities, flocculation
and coagulation processes tend to concentrate most of the heavy
metal content of the incoming wastes into the solid particulate
that is eventually removed as sewage sludge. Stones (2) found
that 28% of the incoming chromium was removed by sedimentation.
In a comparison study he found that removal of chromium was in-
fluenced by the chemical treatment of the sewage. His results
are listed in Table 1. In a later study Stones (3) found that
activated sludge treatment was superior to biofiltration for re-
moval of chromium. He also found an average of 70% removal of
chromium for four different types of activated sludge treatment.
TABLE 1. REMOVAL OF CHROMIUM BY VARIOUS
CHEMICAL TREATMENT PROCESSES (2)
Percent
Process removal
Settlement 22
Calcium oxide (CaO) 49
Sulfuric acid (H2SO
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availability for plant uptake. However, in most cases these
techniques recover <10% of the total metal content.
It is known (6, 7) that a large part of the metal content of
sludge exists as soluble and insoluble metal-organic complexes.
These complexes have not been characterized in detail but are
generally similar to trace metal-organic complexes existing in
soil and involve bonding through principally carboxyl, phenolic
and imide functional groups in the organic matter.
Studies have been made to determine the nature of the organic
content of secondary sewage treatment effluents. Painter
et al. (8) and Bunch et al. (9) found that about 35% of the
organics were ether extractable proteins, carbohydrates, tan-
nins, lignins, and detergents. Rebhun and Manka (10) found that
40-50% of the organic material could be classified as humic sub-
stances (humic, fulvic and hymathomelanic acids) of which fulvic
acid was a major fraction. Gel permeation studies showed that
the majority of the fulvic and hymathomelanic acids had molecular
weights in the range 500-1000, with the majority of the humic
acids being in the range of 10,000-50,000.
Newland et al. (11) have determined the concentration of selected
trace metals associated with various organic fractions of sewage
sludge. The concentrations of Cd, Cu, Mn, Ni, and Zn were deter-
mined in humic acid, 3-humus (insoluble fulvic acid), soluble
fulvic acid, and humin (alkali-insoluble residue) fractions of
sewage sludge obtained by the fractionation procedure described
by Black (12). Their results showed that the organic matter in
sewage sludge had the following composition:
humin 70%
fulvic acid 20%
humic acid 8%
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The trace metal analysis showed that the humic acid fraction
contained the lowest amount of trace metals. They concluded
that contrary to what had often been speculated, the humic acid
fraction is not responsible for large amounts of organically
bound metals. The humin fraction, in general, gave the highest
metal content.
Chromium is commonly found in sewage sludges in concentrations
ranging from 50 to 500 yg/g (13). The nature of this chromium
content has not been well established. It is of considerable
interest, however, since the form in which the chromium exists
has particular importance to the ultimate fate of the chromium
in the environment (e.g., availability for plant uptake,
susceptibility to leaching, or even volatility).
3.1 PROPOSED APPROACH
MRC proposed to conduct four studies to evaluate the chromium
content of a sewage sludge sample.
(A) Total Chrqmium Determination
(B) Organiq E3ftractable Chromium
(C) Humic Material Fpactionation
(D) Aerobic/Anaerobic Digestion
The sewage sludge samples were obtained from the City of Dayton
Guthrie Road sewage treatment plant, located ^1.6 km from the
MRC Dayton Laboratory. This was one of the sites previously
sampled in Task I of EPA Contract No. 68-01-1980 (see Reference 1
for details). Total chromium concentration for the sludge sample
from this site analyzed in the previous study was 620 yg/g.
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3.2 DESCRIPTION OF THE SEWAGE TREATMENT PLANT
The City of Dayton Guthrie Road sewage treatment plant, Guthrie
Road, Dayton, Ohio 45418, was chosen for sampling because the
City of Dayton Water Department personnel stated that the bulk
of chromium waste they receive is handled by this facility. The
plant occupies a site of approximately 640 m x 1280 m. There
are two major buildings on the site, one housing offices and a
laboratory and the second housing the control room and mainte-
nance facilities. Various other small buildings, approximately
20 large trickle bed filters, and several large sludge pits are
also located on the site.
The plant is bounded on the north by Guthrie Road, an open
field and Madden Golf Course; on the east by West River Road,
an open field and the Great Miami River; and on the south and
west by open fields and wooded areas. The closest industry is
on the opposite bank of the Great Miami River and consists of
light industry, an asphalt batch plant, sand and gravel oper-
ations, and storage warehouses.
Guthrie Road sewage treatment plant handles waste from the
City of Dayton and other sections of Montgomery County including
Englewood and Trotwood. The major contributors of chromium in
the wastewater processed by this facility are chrome platers
and large industry such as General Motors and Chrysler installa-
tions in the area serviced.
The plant operates continously and discharges 190,000-230,000
iti3/day of treated wastewater through an open concrete ditch into
the Great Miami River. The average water retention time in the
plant is ^4.5 hours. The outfall is very turbulent and signi-
cantly affects the flow of the river at the point of entry and
for some distance downstream.
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The City of Dayton Guthrie Road sewage treatment plant is located
in southwestern metropolitan Dayton, Ohio area approximately
16 km south of the intersection of Interstates 70 and 75. The
immediate area around the plant site has a relatively low popu-
lation concentration which increases as one moves toward the
Dayton population center. The City of Dayton is located in a
river valley at the junction of the Miami, Mad, and Stillwater
Rivers. The general topography is flat. The metropolitan area
has a population of about 865,000 and supports an impressive
diversity of industry. There are some 850 plants located in
Montgomery County producing over 1000 different products with
an estimated value of over $1 billion annually. Major industries
in the area include automotive subassembly, appliance manufactur-
ing, and precision equipment manufacturing.
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SECTION 4
EXPERIMENTAL
The objective of the experimental portion of this study was to
evaluate the organochromium content of sewage sludge. In order
to more carefully characterize the sewage tratment plant, samples
were taken at various points throughout the plant. The loca-
tions and descriptions of the sampling points are listed in
Section 4.1. The simulated digester experiments performed dur-
ing the study are described in Section 4.2. Fractionation and
extraction procedures are described in Section 4.3. Analytical
procedures including a description of the atomic absorption
detector for liquid chromatography are described in Section 4.4.
4.1 SAMPLING TREATMENT PLANT
Six sites were sampled at the Guthrie Road sewage treatment
plant. Figure 1 shows an aerial photograph of the plant with
the location of the sampling sites. The six sample locations
were the influent, influent to primary, influent to secondary,
influent to secondary clarifier, effluent from secondary clari-
fier, and effluent. These samples were collected in polypropyl-
ene bottles and returned to the laboratory. Each sample was
shaken and a representative aliquot (25 ml) removed. Each
sample was then filtered through 0.2-ym filters and the aqueous
fraction analyzed by atomic absorption.
The filtrates and solids were digested with a 1 to 1 mixture
of concentrated nitric and sulfuric acids in Teflon beakers.
Small quantities of hydrofluoric acid were added to aid in the
10
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D INFLUENT
2) INFLUENT TO PRIMARY
D INFLUENT TO SECONDARY
4) INFLUENT TO SECONDARY CLARIFIER
5) EFFLUENT FROM SECONDARY CLARIFIER
6) PLANT EFFLUENT
GUTHRIE ROAD TREATMENT PLANT
Figure 1. Aerial view of Guthrie Road sewage
treatment plant with sampling locations.
11
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digestion of silica. Results of this study are described in
the Results and Discussion section.
4.2 AEROBIC AND ANAEROBIC DIGESTION
In order to insure that samples obtained from aerobic and anaero-
bic digestion runs were as representative as those obtained from
actual municipal operations, the procedures used in the labora-
tory centered on utilizing biological cultures in use at actual
area waste treatment plantsr
4.2.1 Anaerobic Digestion
Through contact with Mr. Defro Tossey, Superintendent, Division
of Sewage Treatment, Dayton, Ohio, information was gathered to
indicate that the existing anaerobic digesters at the City of
Dayton Municipal Treatment Plant are currently operating on
sludges (entirely primary) that contain high concentrations of
chromium. Thus, a biological culture that was already acclimated
to high chromium levels was available. Quantities of this ac-
climated culture were subsequently obtained and used as the inoc-
ulum for the laboratory run.
Most chromium in the Dayton Municipal Treatment Plant comes from
area metal treating operations. The primary sludge gathered at
the sludge outlet of the primary settling (horizontal rectangular)
tanks thus contains substantial chromium. Quantities of this
sludge were used as feed to the laboratory digester.
The apparatus used in the anaerobic digestion run is shown in
Figure 2. A 5000-ml reactor flask was placed in a water bath
which was heated with an immersion heater. Water temperature in
the bath was maintained through the use of a rheostat to insure
a temperature of 35°C (± 2°C) in the reactor flask itself. The
bath-reactor flask was positioned on a magnetic stirrer to insure
12
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Laboratory
Hood
U)
Magnetic
Stirring Bar
Regulator
Figure 2. Anaerobic digestion experimental apparatus,
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mixing of the reactor contents. The inlet port of the reactor
was fitted with a nitrogen supply (including pressure regulator
and flowmeter) to insure a continuous nitrogen purge through the
system. This was necessary to overcome the potential buildup of
methane gas in the reactor. A tube packed with Tenac GC was
placed in the exit line from the reactor. The Tenax GC resin
would trap any organochromium compounds evolved from the digester
flask.
The actual anaerobic digestion run was as follows: the reactor
was charged with (1) 1500 ml of the anaerobic digester biological
culture, (2) 2500 ml of primary settled sludge, and (3) 500 ml of
distilled water. This sludge mixture was run for 4 weeks with no
additional inputs. The Tenax GC tube was changed after 2 weeks.
After the 4-week run, samples were taken for chromium analysis and
for volatile solid analysis. Before the run, samples were taken
of both the culture and the sludge for the same analysis. The
percent reduction in volatile solids after the run was 56.7%.
4.2.2 Aerobic Digestion
Through contact with plant personnel at the Spauling Road waste
treatment plant, Beavercreek, Ohio, information was gathered to
indicate that the biological media present in the plant's ex-
tended aeration tank would be satisfactory for the laboratory
aerobic digestion run. The treatment plant treats basically
domestic waste but has several industrial waste sources. Quanti-
ties of the biological culture were obtained and used as the
inoculum in the aerobic digestion run. The feed was primary
sludge from the Dayton treatment plant, as used in the anaerobic
digestion run.
The apparatus used for the aerobic digestion run in shown in
Figure 3. A 5000-ml flask was utilized as the reactor. Run at
room temperature, the flask was put on a magnetic stirrer to
14
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Flowmeter -,
Vacuum Pump
Thermometer
Diffuser
Magnetic Stirring Bar
Magnetic Stirrer
•Laboratory Hood
Figure 3. Aerobic digestion experimental apparatus.
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insure mixing. A sparger was placed into the reactor, and a
vacuum pump, connected to both a flowmeter and Tenax GC tube,
was used to pull air into the reactor.
The test procedure was as follows: into the reactor was placed
(1) 1000 ml of biological media, and (2) 3000 ml of settled
primary sludge. Samples for analysis of both chromium and
volatile solids were taken on all fractions both before and after
digestion. The digestion was run for 4 weeks as a batch process
with no additional inputs. Volatile solids analysis indicated
a 42% reduction.
4.3 FRACTIONATION AND EXTRACTION
Newland et al. (11) described a technique for obtaining fractiona-
tion of the humic material for examination of the metal content
associated with the various fractions. The procedure involved:
1) sample drying at 40°C
2) acid washing with 0. IN hydrochloric acid (HCl) to remove
absorbed cations
3) treatment with 0.5N sodium .hydroxide (NaOH) to obtain
alkali-soluble and alkali-insoluble fractions
4) adjustment of the alkali-soluble fraction to a pH of
1.0 with concentrated HCl to precipiate the humic acid
fraction followed by centrifugation and separation
5) adjustment of the remaining solution (total fulvic acid)
to pH of 4.8 with 0.IN NaOH to precipitate the 3-humus
(insoluble fulvic acid fraction)
16
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The four fractions of humus material obtained by this procedure
are:
1) humin (nonalkali-soluble material)
2) humic acid
3) B-humus (nonsoluble fulvic acid)
4) soluble fulvic acid
MRC used a modification of this procedure to attempt to obtain
information concerning the nature of chromium-humus related
complexes. Figure 4 is an overall description of MRC's sepa-
ration scheme. A 50-ml sample of well mixed sludge was centri-
fuged. The supernatant liquid was removed and filtered through
a 0.4-pm cellulose acetate filter. The liquid portion was
retained for analysis to determine the soluble chromium present
in the sewage sludge. The solids from this step were then
shaken with 20 ml of 0.1N HCl. This sample was then centrifuged
and the supernatant liquid analyzed by atomic absorption to
determine the cationic chromium content of the sewage sludge.
These solids were then shaken with the 20 ml of 0.5N NaOH in a
bottle under a nitrogen blanket on a platform shaker for 16
hours. After this period the sample was centrifuged and the
liquid removed. Another 20 ml of 0.5N NaOH was then added and
the sample shaken for 1 hour, centrifuged, and the liquid re-
moved. Finally, a third 20-ml portion of 0.5N NaOH was added
to the solids and the shaking repeated for 1 hour. After centri-
fuging, the liquid portion of the sample was removed. The three
basic liquid extracts were then combined. This solution con-
tained a significant quantity of suspended solids which had not
been removed by centrifuging.
17
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SLUDGE
CENTRIFUGE
FILTER
SOLID
WASH WITH
0. IN HCI
SOLID
SHAKE WITH
0.5NNaOH
SOLID
SHAKE WITH
0.5N NaOH
SOLID
SHAKE WITH
0.5N NaOH
SOLID
HN03/HCI
DIGESTION
LIQUID-SOLUBLE Cr
LIQUID-CATIONICCr
LIQUID
LIQUID
LIQUID
Cr ASSOCIATED
WITH HUMIC
ACIDS
LIQUID {ALKALI INSOLUBLE RESIDUE CHUMIN]
ASSOCIATED Cr )
Figure 4. Separation scheme for chromium in sewage sludge.
18
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In order to accurately determine the distribution of chromium
between the alkali soluble and insoluble fraction, we found it
was necessary to filter the alkali extract. Because of the
slimy nature of the solids this was not an easy chore. We found
it necessary to filter each sample through 10-, 8-, 5-, 2-, 1.2-,
0.8-, 0.45-, and 0.2-ym filters. The various stages were neces-
sary to permit the filtering at smaller pore sizes; otherwise,
the filter pores were very easily plugged. The multitude of
filters resulting from each sample was added to the solid from
that sample and digested in Teflon beakers with concentrated
nitric, sulfuric, and hydrofluoric acids.
4.4 ANALYSIS
All measurements of chromium in the sewage sludge samples were
performed by either atomic absorption (AA) spectrophotometry
or inductively coupled argon plasma (ICAP) spectroscopy. Each
sample was analyzed by digesting the total sample with acid. The
total chromium content of these individual fractions was compared
with the total chromium in the mixtures in the digestion experi-
ments. The instrument and conditions used for the analysis of
chromium in water and the digestion samples are listed in Table 2.
TABLE 2. ATOMIC ABSORPTION CONDITIONS
FOR CHROMIUM ANALYSES
Instrument: Perkin-Elmer Model 303
Lamp: Westinghouse chromium hollow cathode
Lamp current: 15 mA
Wavelength: 357.2 nm
Slit: 0.7 nm
Air flow rate: 25 1/min
Acetylene flow rate: 3 1/min
Recorder: Hewlett Packard 3385
19
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In addition to total chromium determinations by atomic adsorp-
tion, a high performance liquid chromatograph was interfaced
with the atomic absorption spectrophotometer, in a manner similar
to one described by Jones (14). The objective of this coupling
was to attempt to determine the polarity and molecular weight
distribution of chromium-humus acid complexes. The high perform-
ance liquid chromatograph was a Micromeritics Model 7115-24,
which had been modified with a Model 7100-B pumping system. The
interfacing of the HPLC and AA was successfully completed. A
mixture of inorganic chromium ion and three organochromium
compounds was chromatographed on the HPLC chromatograph. The
column used was a Whatman Partisil ODS-1 reverse phase (C-18
terminated) . A gradient program from 100% water to 100% methanol
over a 20-minute period was employed. The chromatographic trace
obtained from the atomic absorption is shown in Figure 5. The
conditions for the HPLC are listed in Table 3; atomic absorption
conditions were the same as those listed in Table 2.
TABLE 3. HIGH PERFORMANCE LIQUID CHROMATOGRAPHY
CONDITIONS FOR ORGANOCHROMIUM ANALYSIS
Instrument: Micromeritics Model 7115-24
Column: Whatman Partisil ODS-1
Mobile Phase A: Water
Mobile Phase B: Methanol
Gradient: 100% A to 100% B in 20 minutes
Gradient shape: Linear
Flow rate: 20 ml/min
Detector: Micromeritics Model 785
variable wavelength ultraviolet
Pressure: ^1500 to 1000 psi
20
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10
u
+ 6
Cr = Chromium (VI) ion
Cr(acac)3 = Tris (acetylacetonato) chromium (III)
Cr(tfa)3 = Tris(trifluoroacetonato) chromium (III)
Cr(pbd)3 = Tris(l-phenyl-l,3-butanediono) chromium (III)
Figure 5. Atomic absorption chromatogram of chromium
in a mixture of organochromium compounds.
21
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SECTION 5
RESULTS AND DISCUSSION
The results and discussion of this report are divided into four
subsections. Section 5.1 describes the results of the analyses
of the samples taken at the six points throughout the treatment
plant. Section 5.2 gives the results of total chromium
analyses of sewage sludge components used in the digestion
studies both individually and as mixtures. Section 5.3 is
devoted to the results of the fractionation of digester samples
before and after the digester studies. This section includes
discussions of the analyses of resin tubes for evidence of
volatile chromium species which may have been formed during the
digester studies. Organic extraction of sludge solids are also
discussed in the third section. Section 5.4 is devoted to the
results obtained during the study for the distribution of 23
elements among cationic, alkali-soluble, and alkali-insoluble
fractions. These results are reported and examined for sludge
samples from both aerobic and anaerobic digestions both before
and after the digestion studies.
5.1 SEWAGE TREATMENT PLANT SAMPLES
The locations of the sites from which the six sewage treatment
samples were taken are shown schematically in Figure 6. The six
samples were the influent to the treatment plant taken at the
degritter, influent to the primary treatment section of the plant
after the preaeration tank, influent to the secondary treatment,
influent to the secondary clarifier, effluent from the secondary
clarifier, and effluent from the plant after the chlorination.
The results of the analyses of these samples for chromium in
22
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to
to
DEGRITTER ^ -PREAERATION
PRIMARY
SETTLING
TRICKLING
FILTRATION
SECONDARY
SETTLING
WASTE
FROM CITY
1. INFLUENT TO TREATMENT PLANT
2. INFLUENT TO PR I MARY
3. INFLUENT TO SECONDARY
4. INFLUENTTOSECONDARYCLARIFIER
5. EFFLUENT FROM SECONDARY CLARIFIER
6. PLANT EFFLUENT
CHLOflJNATION
TO RIVER
Figure 6. Schematic of sampling locations at the sewage treatment plant.
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both the liquid and solid portions of the sample are shown in
Table 4. These results show that while total chromium is re-
duced during the treatment process, the percentage of chromium
in the solids being carried through the plant increases by a
factor of more than five times. This indicates the chromium is
associated with the smallest of the particles in the sewage
sludge.
TABLE 4. DISTRIBUTION OF CHROMIUM THROUGHOUT
THE SEWAGE TREATMENT PLANT
1.
2.
3.
4.
Sample
Influent
Influent to
primary
Influent to
secondary
Influent to
secondary
clarif ier
Sample
size,
ml
25
25
25
25
Cr con-
centration
of liquid,
yg/ml
0.3
0.2
<0.2
<0.2
Solids,
mg/ml
3.34
3.67
0.45
0.50
Cr con-
centration
of solids,
yg/g
551
671
2190
2440
Effluent from
secondary
6.
clarif ier
Plant effluent
25
25
<0.2
<0.2
0.23
0.27
2895
3769
5.2 TOTAL CHROMIUM ANALYSES
The three sewage sludge components used to prepare mixtures for
the digestion studies were analyzed individually for total
chromium. The results of these analyses are shown in Table 5.
After the digester mixtures were prepared, an aliquot of each
was removed and analyzed for total chromium. These same analyses
were repeated after the digester studies were completed. The
results for theoretical and actual total chromium concentrations
24
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are shown in Table 6. These results show amazingly good agree-
ment for samples as seemingly nonhomogeneous as sewage sludge.
TABLE 5. TOTAL CHROMIUM ANALYSIS RESULTS
FOR SEWAGE SLUDGES
Sludge Cr, yg/g
Primary 127
Secondary 9
Anaerobic 98
TABLE 6. COMPARISON OF TOTAL CHROMIUM VALUES,
THEORETICAL AND ACTUAL, OF SLUDGE MIXTURES
Sample sludge
Aerobic
Anaerobic
Theoretical
Cr, yg/g
102
97
Actual
Cr before
digestion,
yg/g
101
105
Actual
Cr after
digestion,
yg/g
99
87
5.3 SEWAGE SLUDGE FRACTIONATION
Using the process described earlier in the experimental section,
the sewage sludge samples were fractionated. This fractionation
process generated a soluble fraction, a cationic (HCl soluble)
fraction, a humus-related fraction (alkali soluble), and a
humin-related fraction (alkali insoluble). The first two
attempts at this processing resulted in very poor mass balances.
These problems were attributed to losses during the filtering
step. Also, information gained during the analysis of sewage
treatment plant samples showed an inaccurate value was obtained
for the alkali-soluble fraction if very fine pore size filters
were not used. This inaccuracy results from the association of
25
-------
the chromium with the small diameter particles. If fxne-pore
filters (0.2 pm) are not used, a larger than actual value xs ob-
tained for the content of the alkali-soluble chromium-containing
fraction.
The results for the soluble chromium content of sludge sample
mixtures from before and after digestion are listed in Table 7.
These results are for both anaerobic and aerobic digestions. As
can be seen the concentrations are low and do not differ signifi-
cantly. Results were also obtained with excellent mass balances
for the other three fractions of the same four samples. These
results are listed in Table 8. The numbers listed for each
fraction are for both AA spectrophotometry and ICAP spectroscopy.
The two techniques show fairly good agreement for the chromium
content. The chromium concentrations are listed as micrograms
per gram of dried sludge. The estimated error for the two tech-
niques was ±10-15%. The alkali-soluble (humus-related fraction)
chromium was found to increase from 7.9% to 8.2% of the total
chromium during the month-long aerobic digestion. For this same
fraction the chromium content decreased from 9.0% to 2.4% of the
total chromium during the month-long anaerobic digestion. This
means that there is little to no significant change in the way
in which chromium is bound in the aerobic process. Second, the
chromium becomes more bound to the larger, less soluble humin
fraction during anaerobic digestion.
TABLE 7. CHROMIUM CONCENTRATION IN THE LIQUID
PORTION OF SEWAGE SLUDGE MIXTURES
Digester mixture Cr, yg/ml
Aerobic before 0.17
Aerobic after 0.15
Anaerobic before 0.20
Anaerobic after 0.16
26
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TABLE 8. COMPARISON OF ATOMIC ABSORPTION AND
INDUCTIVELY COUPLED ARGON PLASMA ANALYSIS
OF CHROMIUM IN SEWAGE SLUDGE FRACTIONS
Chromium, uq/q
Digester mixture
Aerobic before
Aerobic after
Anaerobic before
Anaerobic after
HC1
NaOH
AA ICAP
2
1
1
0
.0
.3
.6
.5
AA
172.
136.
164.
46.
5
8
9
2
ICAP
144
149
166
45.2
Solid
AA
1500
1620
1462
1645
ICAP
1665
1652
1670
1825
AA
1672
1756
1626
1691
Total
.5
.8
.9
.2
ICAP
1811.
1802.
1837.
1870.
0
3
6
7
Initial plans for the program included neutralization of the
alkali fractions followed by HPLC-AA analysis of these neutral-
ized fractions. Unfortunately when the alkali-soluble fractions
were neutralized, a significant portion of the sample precipi-
tated. After filtering the precipitate, the filtrate was found
to be too low in chromium concentration for HPLC-AA. When this
filtrate was concentrated, more precipitate was formed and it
was found to be impossible to increase the chromium content of
the liquid portion to a level sufficient for detection by HPLC-AA.
Similar results were obtained for alkali-soluble fractions which
were adjusted to pH 8. These samples were going to be used with
Sephadex gels for molecular weight determination of the organo-
chromium fraction. However, when concentration was attempted,
the chromium content of the aqueous portion was never high
enough for gel-AA analysis.
Soxhlet extraction of dried sludge samples from the four samples
were conducted with methanol for 24 hours. These extracts were
then analyzed and found to contain no detectable chromium.
The Tenax GC tubes which were used to collect any volatile chro-
mium compounds during the digestion experiments were desorbed
with methanol. A total of four tubes, two from aerobic and two
from anaerobic digestion, were desorbed. Each tube had been
27
-------
used for collection for a 2-week period. The tubes were de-
sorbed with 4 ml of methanol. This volume had been found to be
sufficient for recovery of greater than 90% of most compounds.
Analysis of the methanol desorption solution by atomic absorption
showed no detectable chromium from any of the four tubes. These
methanol solutions were also examined by HPLC-AA and found to
contain ultraviolet-absorbing compounds but no detectable organo-
chromium compounds.
5.4 RESULTS FOR OTHER ELEMENTS
Since ICAP spectroscopy was chosen to check the atomic absorp-
tion results for the chromium content of each fraction, a survey
of the concentrations of 22 other elements was conducted. Table
9 lists the elements and their abbreviations. The results for
the HC1 (cationic), NaOH (alkali-soluble) and solids (alkali-
insoluble) fractions are listed in Tables lOa and lOb. The mass
balances for the elements, except for Ag, Al, B, Si and Ti, are
fairly consistent. These results show homogeneity was obtained
for the sludge samples, and the digestion processes used were
very effective for reducing the alkali-soluble metal content of
sewage sludge.
In order to carry this investigation of the elements one step
farther, a determination was made of the alkali-soluble fraction
content for each element as a percentage of the total concentra-
tion of that element. The results for these determinations are
listed in Table 11. Along with the percent extract in both
before and after digestion sludge samples, the percent change is
listed. The following elements were found to be reduced most by
aerobic digestion: Ag, Al, Cu, Mo, Ni and V. For another group
of elements the anaerobic digestion process results in the
greatest percent decrease in extractability: B, Ba, Cd, Co, Cr,
Fe, Mg, Mn, Pb, Sr and Ti. Finally, some elements did not
undergo a significantly different change in either process: P,
Sb, Si, Sn and Zn.
28
-------
TABLE 9. ELMENTS ANALYZED IN SEWAGE SLUDGE
Element Abbreviation
Silver Ag
Aluminum Al
Boron B
Barium Ba
Beryllium Be
Cadmium Cd
Cobalt Co
Chromium Cr
Copper Cu
Iron Fe
Magnesium Mg
Manganese Mn
Molybdenum Mo
Nickel Ni
Lead Pb
Phosphorus P
Antimony Sb
Silicon Si
Strontium Sr
Titanium Ti
Yttrium Y
Zinc Zn
29
-------
TABLE 10a. CONCENTRATION OF SELECTED ELEMENTS IN FRACTIONS OF SEWAGE SLUDGE SAMPLES
Aerobic .before
HC1
NaOH
Solids
Total
Aerobic after
HC1
NaOH
Solids
Total
Anaerobic before
HC1
NaOH
Solids
Total
Anaerobic after
HC1
NaOH
Solids
Total
Concentration
Aq
8.8
45.0
138
191.8
7.8
28.4
335.3
371.5
6.1
45.9
194
246
2.0
43.3
291
336.3
Al
13.8
1609
4022
5645
7.6
1263
7048
8318.6
9.1
1411
4484
5904.1
_
1157
5417
6574
B
13.6
106.8
426
546.4
6.2
34.0
155
195.2
3.8
99.1
88
190.9
5.0
54
83
142
Ba
1.
27.
184
212.
0.
25
312
338.
1.
30.
291
323
0.
5.
330
336.
Be
4
5
1.4
9 1.4
8
-
2.3
4 2.3
6
4
1.7
1.7
7
4
2.4
1 2.4
Cd
_
64.5
128
192.5
0.03
38
156
194.03
<0.03
68
130
198.03
-
33.4
176.3
209.7
/ yg/g
Co
2.0
14.7
51.5
68.2
1.1
4.7
53
58.8
1.5
6.4
52
59.9
1.4
1.4
60
62.8
Cr
2.0
144
1665
1811
1.3
149
1652
1802.3
1.6
166
1670
1837.6
0.5
45
1825
1870.5
Cu
0.7
391
873
1264.7
0.9
227
1147
1374.9
1.4
427
1088
1516.4
-
262
1205
1467
Fe
4.3
803
10554
11361
0.2
813
9918
10731
3.3
1067
11856
12926.3
1.0
246
11488 .
11735
Mg
1488
93
3751
5332
683
139
4532
5354
831
166
4375
4372
786
89
5018
5893
-------
TABLE lOb. CONCENTRATION OF SELECTED ELEMENTS IN FRACTIONS OF SEWAGE SLUDGE SAMPLES
u>
Concentration, vg/g
Mn
Mo
Ni
Pb
P
Sb
Si
Sn
Sr
Ti
• Y
Zn
Aerobic before
HC1
NaOH
Solids
Total
-
9.3
134.
143.3
-
18.7
49.7
68.4
10
168
416
594
3.6
105
780
888.6
144
5392
10403
15939
3.3
40.3
175
218.6
348
1341
7237
8926
_
254
478
732
16.7
17.1
505
538.8
0,3
46.2
' 1411
1457.5
9.4
31.7
116
157.1
1.1
2383
3805
6189.1
Aerobic after
HCl
NaOH
Solids
Total
1.4
9.4
155
165.8
0.5
7.4
56.7
64.6
15.0
133
500
648
5.5
135
688
828.5
46
4041
12576
16663
1.3
20.8
192
214.1
98
1499
9211
10808
_
151
454
605
26.2
16.7
565
607.9
0.3
46
4055
4101.3
6.3
25.6
174
205.9
0.5
1068
5180
6248.5
Anaerobic before..
HCl
NaOH
Solids
Total
5.5
11
155
171.5
0.4
15.5
51.3
67.2
20.7
136
512
668.7
2.1
141
761
904.1
132
4234
11482.
15848
0.05
26.9
158
184.95
87
1379
6741
8207
0.2
256
373
629.2
57
21
570
648.
0.9
65
2127
2193
7.8
24.6
125
157.4
1.6
1992
4194
6187.6
Anaerobic after
HCl
NaOH
Solids
Total
1.6
2.1
171
174.7
_
10.2
67
77.2
5.3
125
529
659.3
-
88
954
1042
138
3258
12493
15889
-
17.5
205
223.2
67
1098.
5202
6367
0.9
202
446
648.9
35.4
5.4
583.8
624.6
0.02
20.3
3255
3275.32
6.4
22.1
147
175.5
-
966
5450
6416
-------
TABLE 11. DIGESTION EFFECTS ON THE PERCENTAGE OF
SELECTED ELEMENTS IN THE 0.5N NaOH
EXTRACTABLE FRACTION OF SEWAGE SLUDGE
Percent*
Element
Ag
Al
B
Ba
Be
Cd
Co
Cr
Cu
Fe
Mg
Mn
Mo
Ni
Pb
P
Sb
Si
Sn
Sr
Ti
V
Zn
Before
aerobic
digestion
23.5
28.5
19.5
12.9
—
33.5
21.5
7.9
30.8
7.0
1.7
6.5
27.3
28.3
11.8
33.8
18.4
15.0
34.7
3.2
3.2
20.1
38.5
After
aerobic
digestion
7.6
15.2
17.9
7.5
_
19.5
8.0
8.2
16.5
7.6
2.6
5.6
11.5
20.5
16.3
24.3
9.7
13.9
25.0
2.7
1.1
12.4
17.0
Before
anaerobic
digestion
18.7
23.9
52
9.4
_
34.3
10.7
9.0
28.2
8.2
3.1
6.4
23.1
20.4
15.6
26.7
14.5
16.8
40.7
3.2
3.0
15.6
32.2
After
anaerobic
digestion
12.7
17.6
38.0
1.6
_
15.9
2.2
2.4
17.8
2.1
1.5
1.2
15.2
18.9
8.4
20.5
7.8
17.2
31.1
0.9
0.6
12.6
15.1
*Percentages are based on the total concentration of
each element in the undigested, unextracted sludge.
32
-------
REFERENCES
1. Snyder, A. D., D. G. DeAngelis, E. C. Eimutis, D. M. Haile,
J. C. Ochsner, R. B. Reznik, and H. D. Toy. Environmental
i
Monitoring Near Industrial Sites: Chromium. EPA-560/6-77-
016, U.S. Environmental Protection Agency, Washington, D.C.,
June 1977. 135 pp.
2. Stones, T. The Fate of Chromiun During the Treatment of
Sewage. Institute of Sewage Purification, Journal and Pro-
ceedings, London, 1955 (4):345-347.
3. Stones, T. Fate of Metals During Sewage Treatment. Effluent
Water Treatment Journal, 17(12):653-655, 1977.
4. Bradford, G. R., A. L. Page, L. J. Lund, and W. Olmstead.
Trace Element Concentrations of Sewage Treatment Plant
Effluents and Sludges, Their Interactions with Soils and
Uptake by Plants. Journal of Environmental Quality, 4(1):
123-127, 1975.
5. Berrow, M. L., and J. Webber. Trace Elements in Sewage
Sludges. Journal of the Science of Food and Agriculture,
23(1):93-100, 1972.
6. Holtzclaw, K. M., G. Sposito, and G. R. Bradford. Analytical
Properties of the Soluble, Metal Complexing Fractions in
Sludge-Soil Mixtures,: I. Extraction and Purification of
Fulvic Acid. Soil Science Society of America Journal,
40(2):254-258, 1976.
33
-------
7. Sposito, F.f K. M. Holtzclaw, and J. Baham. Analytical
Aspects of the Soluble, Metal-Complexing Fractions in
Sludge-Soil Mixtures: II. Comparative Structural Chemistry
of Fulvic Acid. Soil Science Society of America Journal,
40(5):691-697, 1976.
8. Painter, H. A., M. Viney, and A. Bywaters. Composition of
Sewage and Sewage Affluents. Institute of Sewage Purifica-
tion, Journal and Proceedings, London, 1961:302-314.
9. Bunch, R. L., E. F. Earth, and M. B. Ettinger. Organic
Materials in Secondary Effluents. Journal of Water Pollu-
tion Control Federation, 33 (2):122-126, 1961.
10. Rebhun, M., and J. Mauka. Classification of Organics in
Secondary Effluents. Environmental Science and Technology,
5(7) :606-609, 1971.
11. Newland, L. W., J. R. Ten Eyck, and V. K. Ohr. Organic
Fractionization and Selected Trace Metal Content of Sludges.
Chapter 19 in: Identification and Analysis of Organic
Pollutants in Water, L. H. Keith, ed., Ann Arbor Science,
Ann Arbor, Michigan, 1976. pp. 281-295.
12. Black, C. A. Methods of Soil Analysis, Part 2: Chemical
and Microbiological Properties. American Society of
Agronomy, Madison, Wisconsin, 1965. pp. 1409-1428.
13. Page, A. L. Fate and Effects in Sewage Sludge When Applied
to Agricultural Lands. EPA-670/2-74-005 (PB 231 171), U.S.
Environmental Protection Agency, Cincinnati, Ohio,
January 1974. 107 pp.
34
-------
14. Jones, D. R., IV, and S. E. Manahan. Atomic Absorption
Detector for Chromium Organometallic Compounds Separated by
High Speed Liquid Chromatography. Analytical Letters,
8(8):569-574, 1975.
35
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TECHNICAL REPORT DATA
(Please read /nslructiom on the reverse be fort completing)
V REPORT NO.
EPA-560/6-78-010
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
AN EVALUATION OF THE ORGANOCHROMIUM
CONTENT OF SEWAGE SLUDGE
6. REPORT DATE
JANUARY 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
Paul L. Sherman, Joseph J. Brooks,
Leroy Metcalfe, Thomas J. Hoogheem
8. PERFORMING ORGANIZATION REPORT NO.
MRC-DA-831
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Monsanto Research Corporation
P.O. Box 8 (Station B)
Dayton, Ohio 45407
1O. PROGRAM ELEMENT NO.
II.CbNTRACf/GRANT NO.
68-01-1980
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Office of Toxic Substances
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Task Final 10/77-1/79
14. SPONSORING AGENCY CODE
EPA-OTS
15. SUPPLEMENTARY NOTES
EPA project officer for this study is Dr. John Smith (TS-793)
401 M Street, S.W., Washington, D.C. 20460
16. ABSTRACT
The organochromium content of sewage sludge was evaluated during this
study. Sewage sludges containing chromium were obtained. These sludges
were analyzed to determine total chromium and then fractionated to obtain
four chromium fractions. The fractions represented soluble chromium,
cationic chromium which was dilute acid soluble, and alkali soluble and
insoluble fractions. The two later fractions represent the chromium
which is associated with humus and humin respectively.
Mixtures of the sludges were analyzed for total and fractionated chromium.
These mixtures were then subjected to aerobic and anaerobic digestion for
30 days. After the 30 day period the sludge mixtures were reanalyzed.
Good mass balances were obtained for both the distribution of chromium
among fractions compared with total chromium analyses and between be-
fore and after digestion samples. Data also was collected from the
four fractions described earlier (for twenty-two other elements)
These data were collected for sludge mixtures both before and after
digestion studies. Comparisons were made of the distribution of the
various elements.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
chromium
sewage
sludge
analysis
silver
aluminum
boron
barium
beryllium
cadmium
cobalt
copper
iron
magnesium
manganese
molybdenum
nickel
lead
phosphorus
antimony
silicon
strontium
titanium
yttrium
zinc
atomic absorption
ICAP
COSATl Field/Group
I. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (Thlt Rrportf
Unclassified
20. SECURITY CLASS (This page I
Unclassified
21. NO. OF PAGES
. 42
22. PRICE
EPA Form 222O-1 (t-73)
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