U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
PB-265 006
The Sources and Behavior of
Heavy Metals in Wastewater
and Sludges
Battelle Columbus Labs, Ohio
Prepared for
Municipal Environmental Research Lab, Cincinnati, Ohio
Mar 77
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EPA-600/2-77-070
March 1977
THE SOURCES AND BEHAVIOR OF HEAVY
METALS IN WASTEWATER AND SLUDGES
by
B. W. Vigon, R. A. Craig, and N. A. Frazier
BATTELLE
Columbus Laboratories
Columbus, Ohio 43201
Contract No. 68-03-1177
Project Officer
Robert B. Dean
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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TECHNICAL REPORT DATA
(Please read Imurtietions on tin- reverse before completing)
1. REPORT NO.
EPA-600/2-77-070
4. TITLE AND SUBTITLE
I
3. RECIPIENT'S ACCESSION-NO.
THE SOURCES AND BEHAVIOR OF HEAVY METALS
IN WASTEWATER AND SLUDGES
5. REPORT DATE
March 1977 (Issuing Date.)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
B. W. Vigon, R. A. Craig, and N. A. Frazier
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORG'\NIZATION NAME AND ADDRESS
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
68-03-1177
12. S
K
PONSORJNG AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Cin.,OH
Office of Research & Development
U. S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
16. SUPPLEMENTARY NOTES
16. ABSTRACT
A critical evaluation has been made of the literature regarding the sources of heavy
metals in sludges from municipal wastewater treatment plants. Residential loadings
of heavy metals as a percentage of total metal loads are highly variable with respect
to both the particular element under consideration and the geographic area. Only
rarely is the percentage contribution of any metal attributable to residential source:
greater than one-half the total. The disagreement between studies seems to indicate
that the available information concerning the residential loading estimates may be
biased due to the inclusion of unsurveyed industrial discharges. The sludge content
of heavy metals is frequently correlated with industrial density, but the many
confounding variables make a general statement regarding this relationship impossible
Diffuse sources such as laundries, street runoff and small family-owned operations
may contribute to the discharges from a supposedly residential area. Varying pro-
portions of these minor and essentially uncontrollable sources presumably account for
the high variability in the available data. The contribution of urban runoff to
metal loads of municipal treatment plants is not large relative to other sources at
present, because peak flows are usually bypassed. Local studies will have to be made
to identify the controllable sources of heavy metals whenever their concentrations
in sludge destined for agricultural purposes exceeds acceptable limites because each
community has its own unique mixture of industrial and residential sources.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Metals, trace elements, sewage, sludge
disposal, land reclamation, land utiliza-
tion, industrial wastes, copper, zinc,
nickel, cadmium, cobalt, chromium, lead,
mercury, soil fertility, fertilizers, crops
farm crops, forage crops, grain crops,
jVLant nutrients, toxic tolerances, ground
water, water quality.
8. DISTRIBUTION STATEMENT
Release to Public
b.IDENTIFIERS/OPEN ENDED TERMS
Heavy metals, toxic ele-
ments, trace metals, trac
inorganics, micrbnutrient
micro-elements, sewage
sludge, sewage effluent.,
agricultural land, urban
wastes, residential waste,!
storm drainage.
19. SECURITY CLASS (ThisReport)
Unclassified
20. SECURITY CLASS (Thispage)
Unclassified
c. COS AT l Field/Group
13B
21.
22. PHICt
AoM
EPA Form 2220-1 (9-73)
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DISCLAIMER
This report has been reviewed by the Municipal Environmental
Research Laboratory-Cincinnati, U. S. Environmental Protection Agency
and approved. Approval does not signify that the contents necessarily
reflect the views and policies of the U. S. Environmental Protection
Agency, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem
solution and it involves defining the problem, measuring its impact, and
searching for solutions. The Municipal Environmental Research Laboratory
develops new and improved technology and systems for the prevention,
treatment, and management of wastewater and solid and hazardous waste
pollutant discharges from municipal and community sources, for the
preservation and treatment of public drinking water supplies, and to
minimize the adverse economic, social, health, and aesthetic effects of
pollution. This publication is one of the products of that research; a
most vital communications link between the researcher and the user
community.
The following report is based on a quick literature search and analysis
of available data on the respective contributions of industrial and residential
areas to heavy metals in sludge produced by sewage treatment plants. Although
there is no doubt that high discharges of a heavy metal from an industry will
produce a high concentration of that metal in the sludge, reliable data on the
relative contributions of industry and residential areas is not available. If
heavy metals in industrial discharges are to be regulated to protect crops that
will be grown on the sludge, it is reasonable to ask how much of these same
metals will be contributed by other sources. This report suggests some of
the diffuse sources such as laundries, street runoff and small family-owned
operations that may contribute to the discharges from a supposedly residential
area. Varying proportions of these minor and essentially uncontrollable sources
presumably account for the high variability in the available data. Because
each community is unique local studies will have to be made to identify the
controllable sources of heavy metals whenever their concentrations in sludge
destined for agricultural purposes exceeds acceptable limits.
Francis T. Mayo
Director
Municipal Environmental Research Laboratory
iii
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TABLE OF CONTENTS
Page
SUMMARY viii
INTRODUCTION . 1
RESIDENTIAL CONTRIBUTIONS TO TRACE METAL LOADS .... 3
INDUSTRIAL CONTRIBUTIONS TO TRACE METAL LOADS 9
RUNOFF AS A SOURCE OF METALS IN STP INFLUENT 13
Metals in Street Dirt 13
Urban Runoff 20
THE BEHAVIOR OF HEAVY METALS DURING WASTEWATER TREATMENT 26
THE ULTIMATE FATE OF HEAVY METALS IN SLUDGES USED AS
SOIL CONDITIONERS 40
Toxicity of Heavy Metals to Humans 40
Toxic!ty to the Plant 44
Sludge Treatment of Surface Mine Spoil Banks 44
CONCLUSIONS. 46
PROJECT CONTACTS 48
REFERENCES 52
LIST OF TABLES
Table 1. Comparison of Residential Metal Loading Factors .... 4
Table 2A. Residential Loadings of Heavy Trace Metals as a
Percentage of Total Loadings 4
Table 2B. Industrial Loadings of Heavy Trace Metals as a
Percentage of Total Loadings . . . . 5
Preceding page blank
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LIST OF TABLES
(Continued)
Page
Table 3. Sources of Heavy Metals to Wastewater in
Los Angeles 7
Table 4. Reduction in Metal Content of Sludges Observed
at the City of Chicago-Calumet Plant 7
Table 5. Metals Analysis of Sludge Samples from Domestic
STP's Near Toronto, Canada 11
Table 6. Elemental Composition of Street Contaminants 14
Table 7. Street Dirt: Metal Accumulation Rates and
Particle Size Distribution 15
Table 8. Hypothetical City Parameters. . . . 17
Table 9. Metal Loading from Road Surface Runoff
Compared to Normal Sanitary Sewage 18
Table 10. Metal Loading from Road Surface Runoff
Compared to Normal Sanitary Sewage Flow 18
Table 11. Average Concentration of Metals in Soils from
Sampling Stations in a Large Metropolitan Area 19
Table 12. Metals in Soils in Urban Storm Runoff
Retention Basins 19
Table 13. Total Analysis and Elution of Trace Metal in Soils 21
Table 14. Average, Range, and Standard Deviation of Metal
Concentrations for all Storm Samples: Third Fork Creek
Drainage Basin, Durham, North Carolina 22
Table 15. Metal Concentrations in Base Stream Flow and
Urban Runoff from Subbasins of the Third Fork Creek
Drainage Basin, Durham, North Carolina 23
Table 16. Comparison of Metals in Raw Municipal Waste and
Urban Runoff for North Creek Drainage Basin, Durham,
North Carolina 24
Table 17. Average Daily Metal Loads in New York City STP
Influent from Urban Runoff 25
VI
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LIST OF TABLES
(Continued)
Table 18. Log-Normal Statistics for Heavy Metal Concentration
Ratios in 35 Wisconsin Treatment Plants 28
Table 19. Correlation Between Influent Metal Concentration
and Sludge Concentration 29
Table 20. Predicted Influent Concentrations of Heavy
Metals to Treatment Plants for American Cities 30
Table 21. Comparison of Predicted and Measured Values of
Metals Influent to the Milwaukee, Wisconsin Treatment Plants .... 32
Table 22. Log-Normal Statistics for 35 Wisconsin Treatment
Plants 33
Table 23. Wisconsin STP's Exhibiting Abnormally High or
Low Heavy Metal Concentrations 34
Table 24. Correlation Between Influent Metal Concentrations
and Removal Efficiency 36
Table 25. Comparison of Median and 95th Percentile
Concentrations and Removal Efficiencies for Treatment
Plants in the Interstate Sanitation District Having
Primary and Secondary Treatment 37
VII
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SUMMARY
The major source of toxic heavy metals to municipal wastewater is
a point of controversy. Environmental authorities have proposed pretreatment
of industrial wastes prior to entry into the municipal waste stream with the
objective of reducing the concentration of these heavy metals in the output
of the waste treatment facility. Industry argues that many of these potentially
toxic pollutants are ubiquitous so that the major sources of their entry into
the municipal waste stream are diffuse and they further argue that control
of industrial point sources can therefore result in only marginal reduction
in heavy metal concentration in the waste treatment effluent.
A critical examination of the literature to resolve this point of
contention indicates several relevant findings. Residential loadings of
heavy metals as a percentage of total metal loads are highly variable with
respect to both the particular element under consideration and the geographic
area. Only rarely is the percentage contribution of any metal attributable
to residential sources greater than one-half the total. Furthermore, the
maximum quantity of the most troublesome heavy metal, Cd, which might be
derived from dietary sources (i.e., excluding pipe leaching and food
scraps from garbage disposers) appears miniscule. This fact and the dis-
agreement between studies seems to indicate that the available information
concerning the residential loading estimates may be biased due to the
inclusion of unsurveyed industrial discharges.
The sludge content of heavy metals is frequently correlated with
industrial density, but the many confounding variables make a general statement
regarding this relationship impossible. A more promising approach utilizing
statistical criteria applied to available data or data obtained in a cursory
survey to isolate certain communities or treatment plants for more detailed
study could be employed.
Many older communities are served by combined storm and sanitary
sewers. The effects of urban runoff associated with rain events is of interest
not only for its contribution to the sludge metal content but also for its
implications regarding receiving water management. Present indications are
that the contribution of urban runoff to metal loads of municipal treatment
plants is not large relative to other sources, except perhaps for zinc and lead,
viii
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simply because of the common practice of bypassing a large portion of the
runoff flow. If, however, future management dictates the detention and
treatment of these peak flows, then this source will become a large component
of total loading at times.
With respect to the available analyses of the metal content
sludges, it appears that the generation of accurate influent concentration
data is an impossibility given the present state-of-the-art of modeling the
behavior of metals during treatment. Furthermore, insufficient information
appears to exist to approach this question in a rigorous manner.
The literature on plant uptake/toxicity indicates that plant uptake
of Cd from soils on which sludge is spread generally increases. Studies
which do not show this trend are those where low cadmium sludges are spread
or where incomplete mass balances are performed. Some empirical evidence
exists demonstrating that mechanisms to prevent or delay either the toxic
reaction or the uptake of Cd are present. No theoretical data is available
to elucidate the nature or stability of this complex. Interspecies variability
in the reaction to metal loads is high and present knowledge would dictate
selecting crops which do not concentrate the metals in the edible parts
or else growing nonfood cash crops.
i .
During the course of this investigation conversations with many
knowledgeable persons pointed out the lack of direction in the information
gathering and assimilation process. Bits and pieces of data obtained with
other objectives in mind often were unusable or did not form a cohesive
whole.
IX
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THE SOURCES AND BEHAVIOR OF HEAVY
METALS IN WASTEWATER AND SLUDGES
by
B. W. Vigon, R. A. Craig, and N. A. Frazier
BATTELLE
Columbus Laboratories
INTRODUCTION
During the past decade, the use of digested municipal sludge
as a soil amendment has increased manyfold. The benefits of increased
organic content, greater tilth, and larger yields resulting from the
application of this material are well documented. However, the nature
of the sludging process also results in the retention of heavy metals
contained in the original wastewater. Most often the metals in the sludge
are highly concentrated relative to that in the raw influent.
Opponents to the use of sludge claim, among other things, that
the metals are taken up by plants and spread throughout the food web.
Guidelines addressing this issue have met with mixed reviews. Those who
feel that adequate natural protective measures exist believe that the
present guidelines are overly restrictive and should be relaxed.
In terms of source control to prevent the metals from reaching
the sludge, several options are open. Regulations to require the major
industrial dischargers to treat and remove the pollutants have been
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suggested as a possibility. The counter-argument that diffuse sources are
major contributors to heavy metal loads has also been put forth. It has
been claimed that efforts to reduce metal loads and hence increase allowable
sludge application rates because of pretreatment can effect only minimal
changes.
Consequently, before an informed policy decision can be made, a
critical assessment of the literature on both controllable (industrial)
and non-controllable sources (residential and runoff to combined sewers)
Ls warranted. Funding for such an examination has been provided to
Battelle by MERL.
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RESIDENTIAL CONTRIBUTIONS TO TRACE METAL LOADS
A certain amount of information exists about the contribution of heavy
trace metals to treatment plants by residential sewer users. Investigators in
New York City studied the metal content of sewage from residential subareaB
feeding a treatment plant which also services a large industrial population;
they also sampled sewage from residential areas in other parts of the city at
pumping stations.
(2)
Other investigators measured the trace metals content of sewage at
six sampling sites in predominantly residential areas of Allegheny County PA
(they estimated the nonresidential fraction to be no greater than 10% small
commercial establishments.) The latter report also cited the results of measure-
ments by the Muncie (Ind) Division of Water Quality which sampled waste streams
receiving no industrial discharges at five sampling stations. These researchers
then used this information and other data to infer the relative size of in-
dustrial and residential and, in one case, other contributions to the loadings
of heavy metals in the waste water.
Reference 2 has accumulated the data on loadings of heavy trace metals
for the residential subarea of New York City and the residential areas of Allegheny
County Penn. and Muncie, Indiana and displayed them in terms of pounds per day
per 1000 persons in the area served. We included their Table 1 but have added
a column which includes a weighted average (weighted by average flow) of the
data obtained by sampling other residential areas of New York City.
Using this information and other data, the authors of Ref 1 and 2
calculated the fraction of the total wastewater heavy metal loading which could
be attributed to residential and industrial sources; these are shown in Tables 2A
and 2B, respectively.
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TABLE 1. COMPARISON OF RESIDENTIAL METAL LOADING FACTORS
Residential Loading Factor
lb/Day/1000 Persons
Metal
Cd
Cr
Cu
Pb
Ni
Zn
NY
(Bowery Bay) Allegheny Co.
0.016 0.011
0.08 0.018
0.18 0.10
0,062
0.08 0.012
0.21 0.17
Muncie
0.006
0.007
0.10
0.10
0.02
0.21
NY
(other Resid)
0.002
0.018
0.17
—
0.011
0.23
TABLE 2A. RESIDENTIAL LOADINGS OF HEAVY
PERCENTAGE OF TOTAL LOADINGS
TRACE METALS
AS A
Metal
Cd
Cr
Cu
Pb
Ni
Zn
Mn
NYC Muncie
38
27
38
—
—
2.7
36
10
34 13.3
16
—
17
18
Allegheny
Co.
63
23
96
63
19
32
—
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TABLE 2B. INDUSTRIAL LOADINGS OF HEAVY TRACE METALS
AS A PERCENTAGE OF TOTAL LOADINGS
Metal
Cd
Cr
Cu
Pb
Ni
Zn
Mn
NYC
39
51
19
—
65
20
—
Muncie
—
97.7
67
91.4
88.5
85
75
Allegheny
Co.
NA
—
—
—
—
—
—
Footnote to Table 2.
The data for Muncie, Ind. as presented in Reference 2 added to more than 100% in
some cases. These were taken directly from Reference 2; we believe that these
are the result of combined rounding errors.
Examination of the residential loading data thus presented shows that
the Zn and Cu loadings are sufficiently close that estimates of baseline resident-
ial loadings for these metals of 0.2 and 0.1-0.2 pounds/day/1000 persons, respect-
ively might safely be assumed. Insufficient data is presented about Pb to make
any conclusion. The pattern of variation of data for Ni, Cr and Cd suggest that
some industrial contribution may inadvertantly have been included in the NY,
Bowery Bay data.
The Cd data is particularly interesting as the concentration of this
element relative to that for Zn has been identified as a bellwether of industrial
input to the waste stream. In addition, because of its toxicity and its ultimate
appearance in plants used for human consumption when sludge is used as soil
conditioner, an understanding of the sources of this element is a necessity.
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The natural level of Cd in drinking water in the NY City area
is below the detection limit of the analytical method*; for Allegheny
County it was measured to be 0.0025 mg/1 in a single measurement (the
concentrations of Cu and Zn in NYC tap water are approximately 0.06 mg/1
and 0.03 mg/1, respectively; Ref 1 took the concentrations of other metals
to be zero in their study). This is not at variance with a national
ilysj
(3)
/AY
"average" of 1.4 ppb. The accuracy of the EPA standard analysis for
Cd used for the Allegheny analysis is quoted as being ± 2 ppb.
Assuming this to be the case for the other cities, there is insufficient in-
formation to imply Cd loadings above background for Muncie or the other
residential areas of NYC.
It is possible to estimate an upper bound to the Cd introduced into the
the waste stream as the result of human consumption of foods containing Cd.
There is much uncertainty about the threshold of daily dietary intake of Cd
to produce kidney dysfunction (after 50 years) but no estimates exceed 1000 ug/
(4)
day. If everyone consumed foods containing this level of Cd, a sewer loading
of 0.002 pounds/day/1000 persons would result. Since chronic cadmium poisoning
does not appear widespread, it is safe to assume that the actual daily dietary
intake is much smaller; Reference 4 cites an approximate intake of 100 yg/day.
Thus, for practical purposes the cadmium ingested in foods can be ignored in
attempting to understand the loadings of Cd in residential wastes.
Cadmium does appear as an impurity in zinc; commercial grade Zn con-
tains Cd to the extent of approximately 0.015 percent but can be as much as
0.4 percent. Thus, any cadmium which appears in the wastewater to a greater
extent than this has been used as cadmium or has been selectively leached
from zinc containing materials (the latter is unlikely as Cd is very similar
to Zn and will be expected to leaching a similar manner).
The heavy trace metal percentages attributable to residential sources
as given by Reference 1 and 2 seem to be in contradiction with limited data
available from other cities. Los Angeles performed a study of metals concen-
tration in wastewater from a single upper middle class residential area. With
the caveat that this data may be unrepresentative of residential areas through-
out the city, they found the distribution shown in Table 3 by extrapolation to
the remainder of the city.
* EPA-430/9-75-005.
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TABLE 3. SOURCES OF HEAVY METALS TO WASTEWATER IN
LOS ANGELES
Metal
Cd
Zn
Cu
Cr
Ni
Ag
Residential Percentage
17
25
13
2
12
45
Industrial/Commercial Percentage
83
75
87
98
88
55
The Chicago data is a bit more indirect. In 1969 the Chicago Metropoli-
tan Sanitary District instituted point source control regulations applicable to
industries (primarily platers) which discharged large quantities of heavy metals.
The decreases in heavy metal concentration of the sludge for the City of Chicago
Calumet Treatment Plant are shown in Table 4.
TABLE 4. REDUCTION IN METAL CONTENT OF SLUDGES OBSERVED
AT THE CITY OF CHICAGO-CALUMET PLANT
Percentage Decrease
Metal 1969 - 1974
Cd 72
Cr 62
Cu 81
Hg 35
Ni 92.3
Pb 73
Zn 49
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8
Unfortunately, this data cannot be directly interpreted as implying corresponding
decreases in influent concentration of these metals as the waste treatment process
was changed in the interim. However, additional data shows that the Zn and Cd
loadings of the treatment plant effluent were decreased by the change in treatment
process, implying an increased removal efficiency. Thus, the actual decreases in
industrial discharge are larger than those indicated in Table 4. Nevertheless,
the Chicago data appear to indicate that industrial heavy metal discharges are
more important than References 1 and 2 would seem to show; however, Chicago
also has a typically high concentration of platers.
It would appear that the most likely source of disagreement in the studies
above is the inclusion of the discharge from commercial and small industrial en-
terprises in the residential discharge component. The NY study indicates that
the wastestreams of commercial laundries have large loadings of heavy metals;
the study did not describe the source of these heavy metals in commercial laundry
effluent, however, these are usually ascribed to the soiled industrial, clothing
or toweling being cleaned. It would therefore seem reasonable to assume that
the effluent from smaller laundries in nearby residential areas, street runoff,
and residential effluent may also have wastestreams which reflect the industrial
character of the neighborhood. This point deserves further study.
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INDUSTRIAL CONTRIBUTIONS TO TRACE
METAL LOADS
Use of metals in industry is so widespread as to prevent any meaning-
ful analysis based on the various processes employed. The type and quantity of
metal discharges from industries in a given city or area depends on many factors
including industrial type, process variables, pollution abatement practices and
so forth. The analytical methodology relating to metal quantitation generally
measures total metal content. However, some forms of a given metal are so stable
that for all practical purposes is unavailable for plant uptake and hence
innocuous from a sludge loading standpoint.
Chromium and cadmium are two metals widely used in industrial pro-
cesses. They have also been the subject of some concern regarding plant and
human toxicity effects. In addition some of the environmental chemistry of these
elements is known. Major amounts of hexavalent Cr are thought to be associated
with the metal plating industry. Cr content of wastes from this industry averaged
41 ppm with each plant discharging approximately 2.5 kg daily. These data are
/o\
based on information gathered in 1972 before much of the recent legislation
concerning point source dischargers was enacted. Investigators in Chicago
report a 10-12 percent per year decrease in chromium content of sludges over
the period 1969-74. Also, a portion of the chromium may be discharged to storm
sewers or otherwise not reach the treatment plant. Researchers in New York
found that 15 percent was directly discharged without treatment so that a more
realistic estimate of the amount reaching the plant might be 1.0 kg
per day. This estimate is somewhat in excess of the 0.6 kg obtained in the
New York study but probably gives an estimate of the range likely to be encountered.
Industrial sources of chromium are not limited to metal plating. Cr
is used as a corrosion inhibitor in cooling towers, in anodizing aluminum in
fur dressing, as a tanning agent in the leather industry, in the manufacture
of paints, dyes, and explosives. Trivalent Cr is also used in industry, al-
though less commonly. It acts as a mordant in textile dyeing, is used in ceramics
and glass, and in photography. Thus, an estimation of the contribution of chromium
to waste water from industry must be comprehensive to avoid underestimation. In
addition, many small scale operations may be family-owned making a survey difficult.
Besides the New York study, several other investigators '
identified industrial contributions of Cr as being significant. In parti-
cular, Reference 9 stated the reasons for increasing Cr concentration in
sludges as being due to increasing industry to residential ratios, however,
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10
no description of the plant type or sewer types was included. The treatment
plants were located near Toronto, Ontario, Canada. The Ashbridge Bay plant
receives a complex effluent from a heavily urbanized and industrial area
(Metropolitan Toronto.) The Thornhill plant receives effluent from a small,
basically residential neighborhood possessing a minimum of heavy metal in-
dustry. Other industries, not usually thought of as heavy metal industries,
may be included. The Aurora plant receives effluent from a large town with
a variety of industry, one of which was stated to use chrome extensively.
The concentration values show that the metal content (Table 5) is proport-
ional to industrial density except for manganese, iron, and copper which
are frequently cited as "residential metals".
The research on chromium also manifests the fact that the form
of a metal is tremendously important in determining its environmental signi-
ficance. The ratio of Cr(VI) to Cr(III) in use is very high but the
oxidation/reduction kinetics favor reduction of chromate. This process is
thought to take place during secondary treatment and may result in
substantial alteration of the toxicity since the trivalent oxidation state
is not nearly as hazardous as the hexavalent state.
Industrial uses of cadmium include electroplating, paint, plastic
and battery manufacture, alloying, scrap steel and radiator reclamation,
and several miscellaneous uses. Cadmium is also found as a trace contami-
nant in zinc ores and since the separation is relatively costly, may be
indirectly discharged as a result of industrial zinc processing. An ex-
amination of 1,123 samples of industrial wastes of the Chicago area indicated
that 1.4 percent contained more than 10 mg/1 Cd and 0.27 percent contained
more than 50 mg/1; all these were from metal treatment and plating.
Data from the Chicago area also indicate that the cadmium in sludges
from plants serving the central city is much higher than in sludges from
outlying suburban areas even though the same level of treatment is employed.
While certainly not conclusive, this suggests that treatment plants in
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TABLE 5. METALS ANALYSIS OF SLUDGE SAMPLES FROM DOMESTIC STP'S NEAR
TORONTO, CANADA(a)
r -Lane
Aurora
Thornhill
Ashb ridges Bay
Cr Zn Fe Cu Mn
Percent
1.6 0.94 0.7 0.03 260
0.006 0.11 0.9 0.24 450
0.43 0.58 1.5 0.11 280
Ni
Pb
Cd
ppui
120
25
170
235
185
1425
10
5
45
Reference 9.
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12
residential suburban areas exhibit how cadmium levels because of the lack
of industry. However, many newer suburban areas also have separate sewer
systems in contrast to the combined systems in older central city neigh-
borhoods. Roughly the same correlation exists for Wisconsin communities;
those with known industrial activity show high cadmium levels in the
sludge. The same trend is evident in the data from Reference 9.
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13
RUNOFF AS A SOURCE OF METALS IN STP INFLUENT
Some portion of metals in runoff from sewered areas serviced
by combined sewers can appear in STP sludges destined for land spreading.
Examined in this section are examples of data bearing on sources and
quantities of metals accessible to or in runoff from urban areas.
Over the past few years, a considerable body of information on
metals in runoff has been developed. By and large, however, this infor-
mation pertains mostly to degradation of the body of water receiving the
runoff directly from storm sewers and surface drainage channels rather
than to runoff as an influent to an STP.
Metals in Street Dirt
During dry weather, dirt accumulates on streets. Sources of
dirt include dirt fallout, dirt on vehicles and their tires, and particu-
lates from industrial emissions and vehicular exhausts. For urban areas
served by combined sewers, street runoff can be a source of metals in an
STP influent. The size of this source depends on the capacity of the
(12 13)
treatment plant. Recent studies ' have developed information on
metals associated with street dirt in several U.S. cities. For example,
shown in Table 6 are data on selected metals in dirt samples from urban
residential, industrial, and commercial streets.
The amount of metals in street dirt which may end up in STP
sludge depends upon several factors. These include land use, the rate
and distribution of precipitation, the rate at which street dirt accumu-
lates, STP treatment processes and hydraulic capacity, the strength or
concentration of metals in street dirt, and particle size of solids with
which metals are associated. Data on accumulation rates and particle
size distribution are shown in Table 7. Referring to Part A of Table 7,
two items are noteworthy: (1) lead and zinc accumulate an order of
magnitude more rapidly than the other metals listed, and (2) the wide
variability in accumulation rates.
Part B of Table 7 shows the size distribution of the solids for
each metal species. If one is interested in removing cadmium by street
-------
TABLE 6. ELEMENTAL COMPOSITION OF STREET CONTAMINANTS
(a)
Element
Beryllium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Zinc
Residential
0.2
<2
200
100
2,000
<1
100
100
Industrial
mg/kgW
2
<2
500
100
5,000
<1
100
100
Commercial
0.2
<2
100
100
5,000
<1
50
100
Residential
< . 001
<.002
.24
.12
2.4
<.001
.12
.12
Industrial
Ib/curb mi
.006
<.006
1.4
.28
14
.003
.28
.28
Commercial
<.001
<.001
.029
.029
1.4
<.001
.015
.029
(a) Reference 13.
(b) To convert from mg/kg solids to Ib/curb mile, multiply by the amount of street
solids per curb mile. Note that the time rate of accumulation (Ib/curb mile/day)
is different for each element (see Table 7).
-------
15
TABLE 7. STREET DIRT: METAL ACCUMULATION
RATES AND PARTICLE SIZE DISTRIBUTION
Cd
Cr
Cu
HB
Pb
Ni
Sr
Zn
Total
(Approx.
(a) From
BWl'O.p
(b) Micro
(c) From
A. Accumulation
Rates1'1'
(Ibs/curb mi/day)
Numer- Avg.
leal Dev-
Mean iation
(ra) T m
Cd 0.0014 0.86
Cr 0.050 0.54
Cu 0.15 1.2
Hg 0.016 0.31
Pb 0.38 1.2
Ni 0.018 0.33
Sr
Zn 0.53 1.2
Solids 700 0.89
C. Accumulation Rates versus
Particle Size^ of Solids
(Ibs/curb mi/day) W
104 246
to to
<104 246 495 >495
0.050 0.073 0.017 0
1.0 1.2 0.85 1.95
3.9 4.95 2.25 3.9
5.32 10.64 13.3 8.74
0.41 0.31 0.56 0.52
10.6 13.78 11.13 17.49
) 21.28 30.95 28.10 32.60
Reference (12) . Samples from 4 U.S. cities
ln^ of street.
IIS
Reference (1.3). Sump Jits from 4 U.S. cities
B. % Distributioruby
Particle Slze^'of
Street SolidsUJ
(Each species = 100%)
104 246
to to
<104 246 495
36% 52% 12%
20 24 17
26 33 15
23 17 31
14 28 35
34 12 15
20 26 21
>495 Total
0% 100%
39 100
26 100
29 100
23 100
39 100
33 100
D. % Distribution by Particle
Size^ of Street Solids^6'
(Sum of species - 100%)
104
to
Total <104 246
0.14 0.05% 0.06%
5.0 0.89 1.06
15 3.45 4.38
38 4.71 9.42
1.8 0.37 0.27
53 9.38 12.2
112.94 18.85 27.39
collected from 1 to 13 days
, 2 of which are included in
246
to
495 >495
1.49% 0%
0.75 1.73
1.99 3.45
11.78 7.74
0.49 0.46
9.85 15.49
26.35 28.87
following a rain or
"A".
Total
1.6%
4.43
13.27
33.65
1.59
46.92
100
(d) Computed from "A" and "n". All values have been multiplied by 100.
(e) Computed from "ll".
-------
16
sweeping or by runoff retention basins, then Part B suggests that street
solids in the 104 to 206 micron range contain the majority of cadmium.
It is interesting to note that highest percentages of cadmium and zinc
are associated with different particle sizes.
In Part D of Table 7 the sum of Cd, Cr, Cu, Pb, and Zn present
in street dirt was set equal to 100 percent and the distribution by
particle size computed. If these five metals as a group were of interest,
these data suggest that they are present in about equal amounts in the
104 to 246, 246 to 495, and greater than 495 micron particle size
categories.
Street runoff from rain or snow with sufficient velocity to
transport street solids, if not bypassed or collected in runoff retention
basins for subsequent release to an STP, is an additional hydraulic load
to an STP. During wet weather the volume of the runoff can decrease
concentrations of metals in ah STP Influent, although metal loading rates
as well as total metal loads are increased. On the basis of the hypo-
thetical city described in Table 8, metal loading from street runoff has
(12)
been calculated and compared to normal sanitary sewage (see Tables 9
and 10). Metal loadings from street runoff were computed using overall
averages for street dirt; data on sanitary sewage metals are based on
records from two California sewage treatment plants.
There is evidence (e.g., References 13, 14, and 15) showing an
increase in Pb, Zn, Cd, and Ni concentration in surface soils with
increasing proximity to highways with the contamination being related to
composition of gasoline, motor oil, and tires. Analysis of soils
from 65 sampling stations at street intersections in a large Canadian
city revealed substantially higher lead and zinc concentrations in the
top 2.5 cm soil layer than in the soil at depths between 10 and 15 cm
(see Table 11). The top layer also had higher concentrations of As, Cd,
Cu, and Ni than the lower layer.
On the more general topic of urban runoff, data on concentra-
tions of Cu, Pb, and Zn at various depths in the soils of storm drainage
retention basins are given in Table 12. Note the much higher concentra-
tion of Pb and Zn and to a lesser extent of Cu in the depth interval of
0-5 cm.
-------
17
TABLE 8. HYPOTHETICAL CITY PARAMETERS
(12)
Population:
Total land area:
Land-use distribution:
Residential 75%
Commercial 5%
Industrial 20%
Total street lengths:
Sanitary sewage flow:
100,000 people
14,000 acres
400 curb miles
12 MGD
-------
18
TABLE 9. METAL LOADING FROM ROAD SURFACE RUNOFF
COMPARED TO NORMAL SANITARY SEWAGE (12'
METAL
Lead
Cadmium
Nickel
Copper
Zinc
Iron
Manganese
Chromium
ROAD RUNOFF
(Ib/hr)
600
1.2
10
36
140
7,900
150
80
SANITARY
SEWAGE
(Ib/hr)
0.13
0.0032
0.042
0.17
0.84
54
9.7
12
mo- RUNOFF
'SANITARY
4,600
380
240
210
170
150
15
6.7
* "Hypothetical City" with 0.1 in. rain, lasting for
one hour.
TABLE 10. METAL LOADING FROM ROAD SURFACE RUNOFF
COMPARED TO NORMAL SANITARY SEWAGE FLOW
(12)
METAL
Pb
Cd
Ni
Cu
Zn
f e
Mn
Cr
ROAD RUNOFF
(mg/1)
6.2
0.012
0.10
0.37
,1-4'
83
1.6
0.80
SANITARY
SEWAGE
(mg/1)
0.03
0.00075
0.01
0.04
0.20
13
2.3
2.8
RUNOFF
SEWAGE
210
16
10
9
7
6
0.7
0.3
(from 0.1 in. rain)
-------
TABLE 11. AVERAGE CONCENTRATION OF METALS IN SOILS FROM 65.,
SAMPLING STATIONS IN A LARGE METROPOLITAN AREAC '(ppm)
Depth
0-2.5 cm 10-15 cm
As
Cd
Cu
Ni
Pb
Zn
8.4
2.3
33.2
34.8
292
154
8.2
. 2.1
30.9
30.3
148
115
Note: Sampling stations at major street intersections in a southern Ontario city with population of over 2 million.
TABLE 12. METALS IN SOILS IN URBAN STORM ,
RUNOFF RETENTION BASINS(l*> (mg/kg)(d;
Basins^3'
12 Storm
Drainage
Retention
4 "Control"
Basins
Depth Below
Soil Surface
(cm)
0-5
5-15
15-30.
0-30
Arith.
Mean
19.9
10.7
10.8
17.5
Copper
SD: %
of Mean
13.6
7.5
9.3
16.0
Med-
ian
17
11
16
15
Arith.
Mean
224.8
25.4
17.0
16.5
Lead
SD: %
of Mean
25.0
14.6
9.4
9.1
Med-
ian
165
21
16
15
Arith.
Mean
107.9
38.6
35.5
36.2
Zinc
SD: %
of Mean
24.7
9.6
7.6
11.6
Med-
ian
78
37
35
36
(a) Fresno Metropolitan Flood Control District, Fresno, Calif..
(b) Year basins began receiving runoff ranges from 1962-1971. Grasses planted in some of the basins.
(c) Three of the 4 control basins had been recently excavated and had not yet received any urban runoff.
The fourth was further excavated and a new soil profile was exposed.
(d) Soil profiles obtained by auger.
-------
20
Calling attention to problems of disposal of waste products (in
this case, acidic industrial wastes) Korte, et al., analyzed 10 soils
from seven states for total metals present and then determined the percent
of total metals leached by an acidic solution (see Table 13). Location
of the soil samples was not given, but since Pb was present in only barely
detectable amounts, samples w.ere presumably from rural areas or at least
at some distance from heavily traveled highways. These data are included
here because (1) they show the amounts of metals that can be present in
soils (and therefore runoff) and (2) they shed light on the more general
but related topic of the relative mobility of metals. The order of the
relative amount (as a percentage of the total) of a metal eluted was:
Mn » Co > Ni = Zn » Cu e Cr > Pb = Cd.
Urban Runoff
Among the studies to determine the characteristics of urban
(18)
runoff is that of Colston on the Third Fork Creek 1.67 square-mile
drainage basin in Durham, North Carolina. A total of 521 samples were
taken from subbasins during 36 separate runoff events. Shown in Table 14
are the mean, standard deviation, and ranges in concentration of metals
for all storm samples from the basin. Regression analysis showed the
significant independent variables affecting stormwater quality to be the
rate of discharge and the time from storm start as indicated by the
initiation of runoff. Elapsed time since the last storm was found not
to be a significant factor. A first-flush effect was apparent from a
tendency for concentrations to increase with an increase in rate of
runoff and then decrease as time from storm start increased. A conclusion
of the study was that urban runoff quality did not exhibit significant
variations attributable to land use in the various subbasins. However,
(19 20)
other investigators ' have noted a variation in pollutant loads
with land use. Metal concentrations in storm flow from the subbasins and
land use characteristics of the subbasins are shown in Table 15.
Of primary interest to this study is the comparison of annual
yield of metals/acre of Third Fork Creek drainage basin in raw municipal
-------
21
TABLE 13. TOTAL ANALYSIS AND ELUTION OF TRACE METAL IN SOILS
(7)
Total Analysis
State Ariz
Soil Entl-
Oftier sol
Co . 50
Cr 25
Cu 200
Mn 275
Ni 80
Zn 55
Sand % 71.3
Silt Z 13.7
Clay 2 15.0
Ariz
Alfi-
sol
45
38
60
280
100
70
34.8
18.8
46.4
Ariz Haw
Aridi- Oxi-
soi sol
50
18
265
825
100
85
52.4
37.1
10.5
Note: Moat soils yielded traces of
(a) 1 ml of aqua regia and
After di gust ion 2.0g of
Co Z eluted 2.2
peak ppm 2.0
Cr % eluted (c)
peak ppm (c)
Cu Z eluted 0.4
peak ppm 0. 7
Mn % eluted 41
peak ppm 220
Ni % eluted 1.5
peak ppm 1.5
7.\\ % eluted 1.8
peak ppm 1. 3
Percent
1.3
0.6
(c)
(c)
(c)
(c)
27
40 .
1.8
0.6
2.3
0.6
310
410
260
7400
600
320
23.0
25.0
52.0
Cd and Pb, but
6 ml of HF used for 0.
boric acid added and
of Total
4.4
2.2
(c)
(c)
(c)
(c)
25
225
2.2
1.3
0.7
0.2
Analysis and
33
26
1
1.8
13
8.4
59
1400
24
34
14
13
of Trace Metals (a) ug/g
111
Alfl-
sol
50
55
80
360
110
77
9.5
59.8
30.7
Ind Ky
Molli- Alfi-
sol eol
60
68
83
330
130
100
6.9
58.2
34.9
irregularly and
Ig sample
sample rill
size .
titrj to
30
68
65
950
135
130
3.0
47.1
49.1
only in barely
final volume
Mich
Spade-
sol
25
15
46
80
50
45
91.4
3.9
4.7
NC NC
Ulti- Ulti-
sol sol
120
90
160 62
4100 50
12C 80
110 40
19.0 87.9
19.7. 8.3
61.3 3.8
detectable amounts.
of 50 ml.
Peak Concentration of Metal Eluted
3.2
2.1
(c)
(c)
0.9
0.7
6.4
23
0.8
1.0
1
1.0
33
3.8
0.2
0.1
0.2
0.2
(d)
375
6
3.6
2
0.9
84
4.7
(c)
(c)
(c)
(c)
36
148
5
1.8
38
1,6
7
1.7
(c)
(c).
(c)
(c)
9
6
1.6
(c)
7.3
8.6
30 (c)
11 0.3
6 (c)
2.8 (c)
1.6 0.3
0.9 (c)
68 12
950 18
2.3 1.4
0.7 0.02
2,2 1.5
0,6 0.4
(h) Column.effluents. Leaching solution consisted of 0.025M A1C1v 0.025M FeCl2> and enough HC1 to obtain
pH of 3. Columns lunclicd until effluent concentration of Fe and Al equalled that of Influent,
(c) None of clement detected.
(d) Some samples wore lost.
-------
22
TABLE 14. AVERAGE, RANGE, AND STANDARD DEVIATION OF METAL
CONCENTRATIONS FOR ALL STORM SAMPLES:
THIRD FORK CREEK DRAINAGE BASIN,
DURHAM, NORTH CAROLINA
(Total Solids)
(Total Suspended Solids)
Aluminum
Calcium
Cobalt
Chromium
Copper
Iron
Lead
Magnesium
Manganese
Nickel
Zinc
Mean
mg/1
1440
1223
16
4.8
.16
.23
.15
12
.46
10
.67
.15
.36
Standard
deviation
1270
1213
8.15
5.6
.11
.10
.09
9.1
.38
4.0
.42
.05
.37
Range
Low
194
27
6
1.1
.04
.06
.04
1.3
0.1
3.6
.12
.09
.09
(mg/D
High
8620
7340
35.7
31
.47
.47
.50
58.7
2.86
24
3.2
.29
4.6
-------
23
TABLE 15. METAL CONCENTRATIONS IN BASE STREAM FLOW AND URBAN
RUNOFF FROM SUBBASINS IN THE THIRD FORK CREEK
DRAINAGE BASIN, DURHAM, NORTH CAROLINA(18>
F.-1
£-2 N-l
Sub-Basin
N-2
W-l
W-2
Total
Basin ,
Land Use Characterization
I of Total Acrcs(a)
Population Density/Acre
Stream Length (ft)
Land (I)
Residential
Commercial
Public/Institutional
Unused
Surface Characteristics (I)
. Paved
'Roof Tops
Unpaved Streets
Vegetation
Total Solids
Suspended Solids
Co
Cr
Cu
Fe
«8
Mn
. Nl
Pb
Zn
5.2
13.5
1312
100
0
0
'0
5
7
12
76
358
.82
0.10
0.25
0.10
2.3
13.4
1.3
0.19
0.27
0.13
24.6 17.1
6.9 3.8
3221 ' 3350
50 63
36 6
9 19
5 10
27 16
13 5
3 1
57 78
Average Base
392
20
0.15
0.21
0.16
1.4
17.7
0.50
0.15
0.24
0.15
17.9
1.5
3484
18
44
13
25
33
12
1
54
Flow Concentrations
428
25
0.10
0.30
0.14
1.4
11.2
0.47
0.17
0.21
0.51
15.8
3.5
3282
85
0
15
0
16
5
3
77
(rag/1)
250
20
0.13
0.23
0.11
1.2
11.4
0.42
0.19
0.18
19.4
10.8
2610
73
4
9
14
11
9
6.
74
289
24
0.17
0.26
0.14
2.8
12.4
0.40
0.20
0.19
0.11
100
6.0
59
19
12
10
20
9
3
68
400
SO
0.26
0.23
0.27
1.5
11.8
0.52
0.16
0.26
0.16
Average Concentrations During Storm Flows (ng/1)
Total Solids
Suspended Solids
Al
Co
Cr
Cu
Fc
MR
Mil
Ni
Pb
Sr
Zn
834
627
27
<0.1
0.13
0.11
10
16
0.84
<0.01
0.26
<0.1
0.22
849
638
23
0.1
0.15
0.13
6
10
0.49
<0.1
0.13
<0.1
o.:i2
977
770
22
<0.1
0.16
0.12
5
10
0.51
<0.1
0.32
<0.1
0.27
819
629
18
<0.1
0.13
0.10
10
7.5
1.1
<0.1
0.27
<0.1
0.32
938
739
23
<0.1
0.15
0.12
13
11
0.52
<0.1
0.25
0.11
0.23
1440
1223
16
0.16
0.23
0.15
12
10
0.67
0.15
0.46
0.36
(n) 1069 Acres
-------
24
TABLE 16. COMPARISON OF METALS IN RAW MUNICIPAL WASTE
AND URBAN RUNOFF FOR NORTH CREEK DRAINAGE BASIN,
DURHAM, N.C.(18) (Ibs/acre/year yield)
Metal
Chromium
Copper
Lead
Nickel
Zinc
Raw
Municipal
Waste
7 nf
Ibs Total
0.10 5
0.20 6
<.8 11
<.16 21
1.5 43
Ibs
1.3
1.2
2.5
1.0
1.8
Urban
Runoff
Total
76
67
68
77
51
Total(a)
Ibs
1.7
1.8
3.7
6.3
3.5
(a) Includes metals in base flow of stream; see Table 15.
Note: 100% - (Raw waste % + urban runoff %) = % of total for base flow.
-------
25
waste and urban runoff (see Table 15). Although runoff in the basin
flows to the headwaters of Third Fork Creek, data in Table 16 indicate
that if the runoff were a part of the STP influent, metal loads for the
species indicated would be roughly an order of magnitude greater from
runoff than from municipal waste with the exception of zinc.
Klein, et al., conducted a mass balance study on metals
from various sources in New York City treatment plant influent. Using
average concentrations of metals in 35 grab samples obtained from several
surface areas during rains and estimating the portion of annual runoff
reaching the sewage treatment plants at 95 MGD, the results obtained are
shown below in Table 17.
TABLE 17. AVERAGE DAILY METAL LOADS IN NEW YORK CITY
STP INFLUENT FROM URBAN RUNOFF (!)
(Based on Annual Runoff)
Cd
Cu
Cr
Ni
Zn
~» *-•*"*• — ! B-* .. "~ ' ' -" * -'
Concentration
(mg/1)
0.025
0.46
0.16
0.15
1.6
Runoff
Load (Ib)
19
360
135
110
1220
Percent of
Total Load
12
1.4
9
10
31
Data on metals from.nonrunoff sources determined by Klein, et
al., are given elsewhere in this report. Their results pertaining to
runoff are based on metals on 35 grab samples and whether or not their
values actually reflect a first-flush concentration or a time and flow
weighted concentration of metals in the runoff is one of the main unknowns
in their results. In any event, their approach to determine the mass
balance from nonindustrial as well as industrial sources represents the
type of work that is sorely needed in cities served by combined sewers
for evaluating the need for and effectiveness of industrial pretreatment
as a means of reducing metals in sludges.
-------
26
THE BEHAVIOR OF HEAVY METALS DURING WASTEWATER TREATMENT
The treatment of municipal and/or Industrial wastes involves a
series of unit processes each of which is capable of reducing the oxygen demand
or solids content of the water and producing a stable, disposable sludge.
The sequence of steps and the nature of the physical, chemical, or
biological process involved determines the degree of volatile solids
destruction, the sedimentation of fixed solids and, not incidentally, the
fate of trace metals.
The identification of the behavior of heavy metals during the
treatment process has been acknowledged as a serious need for over 15 years.
The use of treated sludge as a soil amendatory agent has also become more
prevalent and consequently has created new impetus to quantitate the
amounts of heavy metals and determine their physical and chemical charac-
teristics. Until recently, it was nearly impossible to perform valid
analyses on any component of the treatment except the sludge due to the lack of
requisite sensitivities of the laboratory procedures. Routine determination
of metals at the parts-per-billion level were and continue to be beyond
the capabilities of most laboratories. This situation has resulted in
the compilation of a wealth of data on the concentrations of heavy metals
in dried digested sludges but very little information on inflow concen-
trations. A typical comment regarding the extrapolation of these data to
the influent concentrations is that the sludge concentrations generally
reflect the influent values. Such statements sound deceptively accurate.
It is easy to visualize a nearly linear relationship between loading of a
metal to a municipal sewage treatment plant (STP) and the metal content
of a sludge. However, several lines of evidence suggest that attempts to
determine influent concentrations from sludge values will produce erroneous
estimates in the majority of cases.
One technique for estimation of influent concentrations involves
the calculation of the mass of sludge solids resulting from treatment of
(21)
a given volume of wastewater. Another way of visualizing this type
of data analysis is to realize that the sludging process is a combination
of volume reduction and partition equilibrium. In order to calculate the
influent concentration, three parameters must be evaluated, namely, the
-------
27
amount of sludge created per unit volume of wastewater, the chemical or
electrostatic partition coefficient (generally defined simply as a percentage
removal), and the concentration of metal in the sludge. The mathematical
expression takes the form of a mass balance:
Metal in influent = Metal in effluent + metal in sludge
or
V,X = V-Y + GZ
where:
V = Volumetric basis (V^ « V2); usually taken
as 1 liter
X = Concentration of metal in influent
Y = Concentration of metal in effluent
G = Amount of sludge generated per unit volume
of wastewater treated
Z = Concentration of metal in sludge on a
dry weight basis.
This formulation is accurate to the degree that the amount of sludge
generated is known or can be calculated. For each type of treatment scheme,
a sludge generation factor must be determined. In addition, V2Y is often
also unknown, but an assessment of similar treatment schemes or previously
gathered data may permit estimation of the efficiency of removal: •==— .
(6) *•
Concentration datav for four metals, copper, zinc, nickel, and
cadmium, were used to tabulate the central tendency and dispersion.
Sampling, analysis, and compositing methodology is unknown. In order to
observe the magnitude of error associated with such data reduction, the
concentration ratios were calculated; the appropriate log-normal statistics
are shown (Table 18). The spread factors are not unusual for this type of
population. The correlation coefficients for the concentration ratios
(Table 19) show that only in the case of nickel is the pickup by the sludge
significantly and positively related to the influent concentration. Using
the sludge generation factor cited by Reference 22 and the median removal
efficiencies, it was possible to estimate influent concentrations of these
four metals to a number of American cities based on sludge concentrations
supplied in Reference 23. These estimates (Table 20) are well within the
observed range for Wisconsin STP's.
-------
TABLE 18 . LOG-NORMAL STATISTICS FOR HEAVY METAL CONCENTRATION
RATIOS IN 35 WISCONSIN TREATMENT PLANTS(aXb)
Metal Parameter
Cu Geometric mean 6392
Spread factor 2.57
95% Confidence limits 968-42,218
Zn Geometric mean 5567
Spread factor 2.21
95% Confidence limits 1140-27,190
NS
OO
Ni Geometric mean 1799
Spread factor 2.50
95% Confidence limits 288-11,244
Cd Geometric mean 1141
Spread factor 2.94
95% Confidence limits 132-9,862
(a) Reference 6.
(b) Concentration ratio = concentration in sludge / influent concentration.
-------
TABLE 19 . CORRELATION BETWEEN INFLUENT METAL CONCENTRATION
AND SLUDGE CONCENTRATION^3)
Metal r
Copper -0.731
Zinc 0.216
Cadmium 0.372
Nickel 0.996
(a) Reference 6 ' '
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TABLE 20. PREDICTED INFLUENT CONCENTRATIONS OF HEAVY METALS
TO TREATMENT PLANTS FOR AMERICAN CITIES (a)
City
Atlanta, GA
Cayuga Heights, NY
Chicago, IL
Denver, CO
Houston, TX
Ithaca, NY
Los Angeles, CA
Miami, FL
Milwaukee, WI
New York, NY
Philadelphia, PA
San Francisco, CA
Schenectady, NY
Seattle, WA
Syracuse, NY
Washington, D.C.
Cadmium
0.01
<0.005
0.005
0.006
0.014
0.008
0.02
0.02
0.06
<0.005
0.03
<0.005
<0.005
0.009
0.02
<0.005
Nickel
0 . 18
0.04
0.06
0.60
0.11
0.18
0.43
0.49
0.39
0.15
0.46
0.24
0.08
0.16
0.23
_.
Zinc
0.51
0.10
0.21
0.51
0.46
0.30
0.82
0.25
0.24
0.24
1.23
0.11
0.19
0.32
0.33
0.26
Copper
0.22
0.13
0.09
0.21
0.24
0.20
0.44
0.18
0.20
0.29
0.41
0.14
0.14
0 . 18
0.16
0.07
(a) From Reference 23,Concentrations in mg/1.
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31
The only city for which direct comparison with the data in
Reference 6 is possible is Milwaukee. The measured and estimated values
are shown in Table 21. Since Milwaukee has several plants and since this
reference did not state which plant was sampled, data for the two surveyed
are given. Additional information concerning the service area and
facility would be useful in determining the independent variables influ-
encing the pickup process. One point worth noting is that a number of
the plants apparently achieved negative efficiencies. Whether this is
due to recycling of anaerobic digester supernatant coupled with a poor
analysis scheme or to contamination from piping or tanks is not known.
It is felt that log-normal statistics also could be used to
select areas for further more detailed study. This mode of analysis has
been used to treat the information on metals in Wisconsin STP's (Table 22).
It is apparent that not all of the plants exceeding the 95 percent con-
fidence interval do so at all three measurement points. Also of interest
is the fact that the cities noted as being out of range are different
for each metal (Table 23).
i
The results of some limited research to correlate the efficiency
t
of metal removal with the type of treatment practiced at a given plant
(11) !
have been published. One study routinely monitored the efficiency
of heavy metals removal in six STP's in midwestern cities. Four basic
plant types were included:
(1) Primary with sludge digestion
(2) Primary with vacuum sludge filtration
(3) Trickling filter secondary with sludge digestion
(4) Activated sludge secondary with sludge digestion.
None of the sludges from these plants is landspread so no digested
sludge samples were analyzed. Influent, final effluent, and primary sludge
composited samples were collected from all plants and secondary sludge
samples from those plants practicing secondary treatment. Compositing was
performed over a 2-week period taking flow variations into consideration
so that diurnal variability should be partly averaged'. There appears to
be little correlation between heavy metal removals and plant size or
population served. A recalculation of data supplied by these authors did
show a slight (r = 0.562; P < 0.15) correlation between percent metal
-------
TABLE 2 L. COMPARISON OF PREDICTED AND MEASURED VALUES
OF METALS INFLUENT TO THE MILWAUKEE, WISCONSIN
TREATMENT PLANTS
Metal
Cu
Zn
Ni
Cd
' f \
Predicted Concentration
0.20
0,24
Q.39
0,06
Measured
Jones Is.
0.07
1.00
0.12
0.06
Concentration, mg/1
South Shore
0.48
0.68
0.20
<0.02
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TABLE22 . LOG-NORMAL STATISTICS FOR 35 WISCONSIN TREATMENT PLANTS
(a)
Metal
Cu
Zn
Ni
Cd
/ Parameter
Geometric Mean
Spread Factor ... -.
95% Confidence Limits ^ }
Geometric Mean
Spread Factor
95% Confidence Limits
Geometric Mean
Spread Factor
95% Confidence Limits
.Geometric Mean
Spread Factor
95% Confidence Limits
Influent
0.10
2.62
0.01-0.69
0.42
2.11
0.09-1.87
0.10
2.68
0.01-0.72
<0.02
2.01
<0. 005-0. 08
Effluent
0.06
2.20
0.01-0.29
0.19
2.45
0.03-1.14
0.09
2.44
0.02-0.53
0.01
1.75
0.003-0.03
Sludge
696
2.48
113-4281
2332
2.04
560-9705
111
5.06
4.33-2842
30
3.23
2.78-312
(a) Data from Reference 6
(b) Means and Confidence Limits in Parts Per Million
-------
TABLE 23 . WISCONSIN STP'S EXHIBITING ABNORMALLY HIGH OR LOW
HEAVY METAL CONCENTRATIONSCa>
Plant
Eau Claire
LaCrosse
Milwaukee
(South Shore)
Neenah
Waukesha
No. Fond du Lac
Wisconsin Rapids
Fond du Lac
Ripon
LaCrosse .
West Bend
Metal
Cu
Cu
Cu
Zn
Zn
Ni
Ni
Cd
Cd
Cd
Cd
Sample Point
Influent, effluent,
sludge
Effluent
Effluent
Sludge
Sludge
Influent, effluent
sludge
Effluent
Influent, effluent
Influent , effluent
Effluent
Sludge
Exceeded Limits on Low or High
Side of Distribution^)
High
High
High
Low
High
High
High
High
High
High
High
(a) Reference 6
(b) Based on 95% confidence limits; n = 35.
-------
35
removal and total metal loadings. However, analysis of the relationship
between removal efficiency and the influent concentration of a particular
metal showed no consistent trend (Table 24). The correlation coefficients
for two of the metals, copper and zinc, were highly positive in accord
with these authors' original contentions. The coefficients for cadmium
and mercury are slightly significant and positive; that for lead is
insignificant. The correlation of chromium concentration with removal
is slightly significant and negative! By averaging the data these inves-
tigators obscured the differences in behavior between the metals.
It was claimed that the secondary treatment plants achieved
higher removal percentages possibly because of the adsorption of the
metals onto the biological floe. Without disagreeing with these con-
clusions, it would be more defensible to suggest a mechanism for the
removal process by performing additional studies of a theoretical nature.
Calculations of the solubility of metal hydroxides(22) showed that if a
o i Oj_
solid phase was present it alone could reduce dissolved Cu , Pb , and
Cr concentrations to approximately 1 mg/1. However, no soluble
complexes other than hydroxides were considered. The competition of
other ligands for the metal ion and the effect of the presence of other
solid phases thermodynamically stable in the pH range 6.5 - 9 were also
not examined. Considerations of solid metal carbonates, oxides or mixed
anion complexes could alter the solubility relations substantially. The
effects of organic chelators on the solubility of trace heavy metals has
been noted' >^' but not examined in this context. Likewise little
theoretical evidence was provided for attributing the generally higher
removal for STP's practicing secondary treatment to an adsorption
mechanism on the microbial floe formed during the activated sludge process.
The observation of higher removals during secondary treatment has been
noted by other authors as well^22»2^>25).
Reference 26 attempted to show differences between primary and
secondary plants by means of a cumulative frequency distribution. The
data (Table 25) indicates first that in order to make valid statements
about the relationships between influent and sludge concentrations, more
sensitive analytical methods must be employed. For example, the true
median cadmium concentration may be only slightly less than the detection
-------
36
TABLE 24. CORRELATION BETWEEN INFLUENT METAL CONCENTRATIONS
AND REMOVAL EFFICIENCY(a)
Metal
Pb
Cu
Cd
Cr
Zn
Hg
Total Metal
Concentration
r '
0.189
0.817
0.379
-0.355
0.780
0.542
0.562(b)
(a) Data from Reference 11.
(b) Author's' value is 0.945.
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TABLE 25. COMPARISON OF MEDIAN AND 95TH PERCENTILE CONCENTRATIONS AND
REMOVAL EFFICIENCIES FOR TREATMENT PLANTS IN THE INTERSTATE
SANITATION DISTRICT HAVING PRIMARY AND SECONDARY TREATMENT
(a)
Median Concentration
Metal
Copper
Zinc
Chromium
Lead
Nickel
Cadmium
Mercury
Plant Type
Primary
Secondary
Primary
Secondary
Primary
Secondary
Primary
Secondary
Primary
Secondary
Primary
Secondary
Primary
Secondary
Influent
0.10
0.10
0.20
0.16
<0.05
<0.05
<0.20
<0.20
<0.10
<0.10
<0.02
<0.02
0.0012
0.0013
Effluent
0.10
0.05
0.18
0.08
<0.05
<0.05
<0.20
<0.20
<0.10
<0.10
<0.02
<0.02
0.0009
0.0009
Percent
Removal
0
50
10
50
—
—
—
—
—
' —
—
—
25
31
95th Percentile
Influent
1.15
0.40
1.56
0.54
0.50
0.35
0.60
<0.20
0.60
0.30
0.04
0.02
0.0088
0.0080
Effluent
0.65
0.25
1.42
0.26
0.45
0.15
0.40
<0.20
0.50
0.20
0.06
0.02
0.0100
0.0059
Percent
Removal
44
38
9
52
10
57
33
' —
17
33
—
0
—
25
(a) Reference 26Concentrations in mg/1.
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38
limit. In this case a concentration factor of only about 500 would cause
the cadmium concentration in the sludge to exceed the 10 mg/kg guideline
for land application. Secondly, it was stated that primary treatment
plants achieved poorer removal of heavy metals. Clearly, this statement
cannot be supported statistically for the median concentrations of all
the metals listed except copper and zinc. These authors also stated that
the primary plants served largely industrial users while secondary plants
received predominantly residential contributions and only a small amount
of industrial waste (percentage not estimated). At the median concentra-
tion there is little difference between the influent concentrations of
any of the metals. This indicates that the majority of industrial users
are not discharging high concentrations of heavy metals, that the con-
centrations discharged by the industrial contributors to the secondary
plants are very high, or that only some (<50 percent) of the primary
plants are dominantly industrial. At the 95th percentile, all metals
demonstrated higher influent concentrations in the primary plants sug-
gesting that a relatively few plants served industries who were dis-
charging metals (assuming that the original relationship between primary
plants and industry is valid and that primary plants serve areas which
have approximately the same quality of residential or urban contributions)<
In fact, this last condition may not be met for heavily industrialized
areas since these areas may also have high street runoff loads. The data
is insufficient to arrive at a definite conclusion.
One study(^') was located which at least identified the types
of metal responses expected for different metal-solid interactions. It
was stated that, in general, processes depending solely on precipitation
should yield a metal residual dependent only on the solubility product of
the metal precipitate and complex formation (assuming that kinetic control
can be ruled out). It was also correctly pointed out that, if suspended
solids are not completely removed, then a portion of the metals associated
with the fine particles will contribute to measured metal residuals even
though the concentration in true solution is reflective of equilibrium
conditions. If adsorption isotherms for various metals indicate that
such a mechanism may dominate, then residuals should have a tendency to
increase with an increase in influent metal concentration because of the
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39
asymptotic relationship between concentration and amount adsorbed. The
actual mechanism probably contains elements of both models. In regards
to increasing metal removal in a given unit process, the mechanism of
removal is of secondary importance to the understanding of the process
variables. However, to assess the partition of heavy metals between
solid and solution phases, knowledge of the mechanistic aspects is
essential.
The Metropolitan Sewer District of Greater Cincinnati performed
a limited study in 1974, monitoring the influent concentrations of heavy
metals to four plants in the District' '. These data seem to group
naturally into two sets. The median concentrations for Cr, Zn, Cu and Ni
from the Mill Creek and Little Miami Plants are very comparable and
exceed the median concentrations at the Sycamore and Muddy Creek Plants
by factors ranging from two to six, depending on the metal. The reasonable
conclusion is that the former two plants have a higher percentage of
industrial dischargers. Sewer district personnel confirmed that this was
indeed the case with the Little Miami and Mill Creek Plants having a
large number of metal platers within their service areas. The Muddy Creek
Facility was thought to be affected only marginally by industrial dis-
charges and the Sycamore STP influenced not at all in this regard.
One other point concerning these data is of interest. At the
Mill Creek Plant, which serves an area sewered by a combined system,
rainfall was noted on Friday and Saturday, September 27 and 28. A total
of 0.92 inch was recorded at the Cincinnati Observatory. Average daily
flows (ADF) on these days were 107 and 130 mgd, respectively. The follow-
ing week was dry and influent concentrations of the aforementioned metals
on Friday of that week were higher for Cr, Zn, and Ni and only slightly
lower for Cu. On Saturday, the concentrations of all four metals were
far lower than they had been the previous week or even the previous day.
On these days, 117 and 107 million gallons of wastewater were treated.
Although it is difficult to statistically justify judgements based on
such a small sample, the trend appears to support the hypothesis of
Friday discharging by Industries and also shows that urban runoff is
perhaps oT significance in increasing concentrations above base levels.
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40
THE ULTIMATE FATE OF HEAVY METALS IN
SLUDGES USED AS SOIL CONDITIONERS
The problem of the ultimate fate of heavy trace metals in sludge
used as a soil conditioner has two distinct parts. On the one hand, there
is the question of the phytotoxicity due to increased metal content of the
sludge amended soils; on the other hand there is the question of the effect
of changes in plant composition upon the animals consuming the plants.
Toxirity of Heavy Met^ils to Humans
A discussion of human metal toxicity due to plant uptake from
sludge reduces to a discussion of cadmium. The toxic metals mercury and
lead found in sludge do not show up in toxic concentration in the consumable
(29)
parts of plants. Other elements known to build up toxic concentrations
in plants, as, for instance, selenium, are not usually found in sewage sludge.
In corn grown under normal conditions it has been shown that these heavy
trace metals which do appear in the grain nrc concentrated in the germ of
the grain. For instance, essentially all the Zn and approximately 70%
of the Cd appear in the germ which represents 12% of the whole grain. Since
the germ of corn which is used in processed foods is separated from the
remainder of the grain (part to be pressed for oil and the remainder used
as cattle feed), the possibility of the careful use of grain with an excess
heavy metal concentration exists.
Cadmium is extremely toxic in humans; the normal human body burden
is 15-30 mg for an adult, approximately half of which is in the liver and
kidney. ' A concentration of approximately 2QO ppm in the kidney appears
to ho the threshhold Level value for kidney dysfunction. Cadmium absorbed
into the body has a residence time (half-life) of about 40 years. Attempts
at mass balance calculations to determine a threshhold level of dietary intake
-------
41
to produce kidney dysfunction after 50 years of consumption are frustrated by
uncertainties in the actual absorption rates of ingested Cd and the normal
loadings of Cd in the body. The range of possibilities within the present
(4 )
state of our knowledge is between 100 and 1,000 ug/day. This allows a
safety factor in our current dietary dose rate of somewhere between unity and
thirteen. It is fairly clear that the lower value is too small as it is close
to the present average dietary intake and chronic Cd toxicity does not appear
widespread. Nevertheless, the safety factor is small and unknown so that any
additional input of Cd into the human diet should be viewed with concern.
Cadmium uptake by plants from sludges applied to the soil is a
very complicated phenomenon. As a generality, the only statement that can
be safely made is that increasing the soil Cd content will effect a change
in plant Cd in the year the sludge is applied. Furthermore, the relationship
is linear with the added soil Cd ' to well beyond the point at which Cd
toxicity causes major reductions in the yield from the plants. The slope of
this curve depends on a number of factors, including but not necessarily
(29)
restricted to:
• Soil pH
• Plant species (and variety)
• Plant part considered
• Temperature
For instance, lettuce which picks up about 10% of the added Cd in slightly
acid, sandy soil, and chard accumulate more Cd than do peas. In peas the seed
picks up a larger percentage than the foliage; in radishes, more Cd will be
found in the leaves than in the root.
To date the review of the available literature shows insufficient
information to make definitive statements about Cd concentrations in plants
on sites on which municipal sludge has been spread for long periods of time.
California experience " has involved the land application of sludges for
-------
42
over 30 years with no indication of Cd toxicity problems. These have, however,
involved sludges from relatively primitive treatment methods; more advanced
methods may deposit a larger fraction of the heavy metals in the sludge, so
this situation may change. The Calumet Treatment Plant of the Chicago
Metropolitan Sanitary District found that in going to anaerobic digestion
from lagoon settling, essentially all the Cd is retained in the sludge and
the Zn carried away by the effluent is halved.
One of the longest experiences with landspreading is the land
treatment system at Werribee, Victoria, Australia (treating Melbourne's
waste) which has been in continuous operation since 1897. This
system has been a raw sewage treatment system but its experience with heavy
metal should be indicative of the long term effects of spreading sludges on
agricultural land. Unfortunately, only a very limited amount of data exists
on the heavy metal loading in the influent. For instance, there is only
one sample for which lead was measured and only three for cadmium; the latter
measurements varied by more than a factor -of ten so that it is difficult
to determine which of these, if any, are representative. The other heavy
metal data represents the June, 1968 through November, 1969 period only.
Thus there is no long term data on heavy metal loadings.
With this important caveat in mind, the results of the Werribee
experience indicates no increases of heavy metal loadings to toxic levels.
All trace elements in the soil appear to have been increased (relative to
an unirrigated control) as did the extractable amounts of these elements.
These have increased in some cases to values outside the range of normal
values for soils. In some areas the trace elements Zu, Cu, Cd, Cr,
and Ni were noted in the forage grasses grown on the treated land although
in no case was the increase to a level toxic to livestock; in some cases,
a decrease (Cd in one 73-year old sample and Mn in each sample) was noted.
The variation between samples grown on treated soil and those grown on the
control is sufficiently large that no definitive statements can be made
regarding the effect of long term treatment of land with sewage.
-------
43
The results of the Werribee experience are ambiguous. On the one
hand, no serious heavy metal problems have occurred as a result of more than
70 years of application of sewage to the soil. On the other hand, the avail-
able data is insufficient to tell us why no problems have arisen.
Most of the reports show increased Cd uptakes on soil treated with
(29)
municipal sludge; exceptions include areas treated with low Cd sludge and
an Illinois study. In the former study, grasses on the Hagerstown sludge
farm Which has received (low cadmium) sludge for 24 years show elevated Zn
contents but Cd levels unchanged relative to control areas. In the latter
study, the investigators found the trace metal uptake in corn and soybeans,
to be a function of the total metal deposited during the current growing
season and independent of the total deposited metal from earlier growing
seasons. This has been observed by others and appears to indicate that
annual loadings of Cd are more important than the total loading over a
number of years.
Studies with c.hard indicate that plants grown on soil treated
with composted sludge show less Cd uptake than those treated with fresh sludge.
It isn't clear exactly what aspect of the composting operation is responsible
for the difference in Cd uptake but the composted sludge has a much higher
pH than uncomposted: low pH tends to increase plant uptake of Cd. There is
also the possibility that, in composting the organic matter chelates heavy
(09) (35)
metals , thereby making them unavailable to plants. Other observers
have noted, however, that metal availability is more complicated than a simple
question of water solubility. It has also been observed that direct application
of the heavy metals without the accompanying organic matter characteristic of
sludges leads to higher immediate plant reactions. There is no evidence
as to the mechanism which prevents or delays the plant reaction to the heavy
metal nor any indication as to the persistence of this protective mechanism
over a period of time after the application of the sludges.
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44
Toxicity to the Plant
Sludge amended soil need not be used to raise crops for human
consumption (nor for consumption by livestock); a disposal farm might, for
instance, be dedicated to growing Christmas trees or hybrid poplars for
pulpwood. In such a case, the toxic reaction of the plant to the heavy
metals in the sludge is more important than the uptake of metals toxic
to humans.
The question of plant toxicity to heavy metals is very similar to
that of plant uptake. The metals involved in sludge are most likely Zn, Cu,
and Ni; Pb could be toxic but the PO, in the sludge apparently acts to make
the Pb unavailable. Phosphate is thus a helpful component of the sludge
(29)
as it also helps to make Zn unavailable; however, in some cases,
phasphate concentrations and phosphate toxicity may be the limiting
factor in sludge application rates.
The factors relating to sludge toxicity are basically the same
as those for plant uptake except for the variation of the toxic effect
with metal. In general, lowering the pH increase, the availability, as
does a high C.E.C. Individual crops will vary considerably in their
ability to tolerate heavy meatls as will varieties within species.
Sludge Treatment of Surface
Mine Spoil Banks
The application of sewage sludge to surface-mined areas produces
beneficial effects. In most cases, even if attempts at reclamation have
been made, the topsoil has been lost or mixed with other overburden in the
strip mining operation. The surface soil then is typically sufficiently low
in pH and high in toxic metals that few vegetative species can grow on it.
Treating this soil with municipal sludge improves growing conditions in
several ways. Typically the addition of sludge raises the pH of the soil,
introduces organic matter, and introduces considerable quantities of phos-
/ q£ \
phate; each of these tends to make the existing metal concentration less
available to the plant. In an experiment in which corn was grown on sludge
-------
45
amended strip mine soil, the heavy metal concentration of the corn was higher
/ O £ \
in the control than in the test plot (This was ascribed in part at least
to the growth under stress conditions as the. control yield and quality were
each very poor.) In other experiments with grasses and leaves, the metal
concentrations varied from "normal to moderately high" and was very species
(37,38)
dependent.
From the literature reviewed, it is not possible to make many
definitive statements about the long term effects of sludge application to
cropland in terms of build up of toxic metals. Since the factors for Cd
uptake are so many and the functional dependence so poorly known, an ex-
tremely conservative point of view would appear prudent for sludge spread-
ing on land with crops intended for human consumption. Because of success-
(29)
ful results in some experiments in this area (the Hagerstown experiments
and the Illinois work )more work must be done. In each of these experi-
ments the metals have been applied to the soil. They have gone somewhere.
If not into the plant—where? Have they in some way been made inaccessible
to the plant while remaining in the soil or have they been carried off in
surface water. A careful mass balance of applied metal, absorbed metal,
and soil metal buildup must be made. If some mechanism has made these
metals inaccessible to the plant, what is this mechanism and what are the
limits on its operation? Can these crops safely be used for feed for
livestock? These first-order questions need to be answered.
Second order questions which also should be considered include:
• What synergisms or antagonisms exist between the
various trace metals?
• How do the heavy trace metals revert to forms in-
accessible to plants? Can this process be
stimulated artificially?
The application of sludge to surface mined land appears to be an
attractive concept, since it can make unproductive land productive.
Since the problem in this case can be pre-existing excess heavy metals
concentrations careful monitoring of food stuffs grown on such soils would
be needed. Consideration of dedicating such land to non-food crops might
be given.
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46
CONCLUSIONS
The foregoing analysis points out one fact clearly. Unless
additional insight into the process of pickup of metals by waste-
activated sludge is gained, little use can be made of the data base on
metal content of sludges. Frequently, cities showing high influent
concentrations achieve sufficiently poor removals that sludge con-
centrations of a given metal do not exceed statistical criteria of
abnormality. In such cases effluent discharge criteria may be needed
to protect downstream water quality. On the other hand, the concentra-
tion ratios of certain treatment plants may be high enough to cause
concern over metal content of the sludge, even though inflow values may
not indicate that a problem exists.
Attempts to fill in gaps in data by extrapolation can
only yield approximations due to tlit' complexity and nature of inter-
actions between heavy metals and solid surfaces. Operating policies of
individual STP's also cause difficulties in estimation because of
recycling, poor sampling design, or contamination. The options might
include a requirement to establish more precise mass balances of heavy
metals in those areas where statistical criteria indicate a need. The
calculation of the geometric mean of expected within-plant metal removal
performance (as concentration ratios or fraction removed) may allow the
use of previously collected information on metal concentrations in
sludges; alterations in process variables or influent metal characteristics
would necessitate a reevaluation of plant performance. High influent or
sludge concentrations of certain heavy metals may very well point to an
industrial discharger, but, lacking additional information, any conclu-
sions must be qualified.
Although a number of studies were located which examined the
effects of tertiary treatment (generally using lime or alum) on effluent
trace heavy metal concentrations1 ' '3 , little consideration has been
given to the increased sludge metal loads or to the disposal of the in-
creased volumes of sludge which will be generated.
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47
In total, it appears that regulation of industrial dischargers
will, in fact, produce reductions in the levels of heavy metals in both
sludges and effluents. On the other hand, a blanket statement covering
all industries known to utilize or discharge heavy metals would be very
costly from the standpoint of enforcement as well as treatment.
Other alternatives are available. In some areas, sludges may
have a low metals content even though some industrial loading occurs.
Some means of distinguishing these situations is clearly necessary since
it cannot be documented that improvements will result in every case when
limits are set on industrial discharges.
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48
Project Contacts
George Walkenshaw, Columbus, Ohio - Columbus monitors the influent
to and effluent from the treatment facility and the effluent from all In-
dustries which have toxic or strong wastes. The purpose of this program
is to establish appropriate surcharges for BOD, nitrogen, phosphorus, and
suspended solids. At present there are no plans to include toxic materials
in the surcharge scheme as there is no evidence that they increase treatment
costs.
Robert Carter, Canton, Ohio - Canton monitors the metal content
of the influent, effluent, and sludge produced at their STP. They find
approximately 200 ppm Cd in their sludge but do not detect—by their measure-
ment technique (AA)—Cd in the influent. They do have volumetric metering
on most of the local industries and do take periodic samples of effluent
for testing. These data they regard as proprietary to the industries in
question but could be made available with the appropriate EPA groundwork.
The utility of these data might be slightly questionable as among the in-
dustries which are currently not metered are Canton's two largest industries.
Stanley Whitebloom, Coordinator of Industrial Wastes, Chicago Metro
Sanitary District - Chicago requires point source pretreatment for big platers.
He felt platers were the main source of heavy metals, or rather, main control-
lable source. They have a great deal of data on this particular source. They
have some sketchy information on runoff and influent to treatment facilities,
but do not feel it is defensible in a mass balance. Chicago has more than
5500 miles of sewer to which the exact number of hookups is not known with
any degree of accuracy. The Sanitary District staff believes other industrial
sources and street runoff are probably significant in themselves, since tight
regulation of platers has resulted in only moderate reductions in sludge metal
content.
Several suggestions were made with regard to research needed prior
to policy formulation:
(1) More information is needed on the relationship, if any,
between metal concentrations in sludge and plant uptake/
human health effects.
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49
(2) Agreement should be reached between guidelines being
promulgated by EPA and the Department of Agriculture,
respectively.
(3) Mass balances should be required only in special cases
since to perform an adequate study for a city like
Chicago would be prohibitively expensive.
(4) If a single number is to be stated as a maximum sludge
concentration or loading, then the reasoning behind the
stated value should be published in detail so it can be
supported by subsequent experimentation.
Dr. Cecil Lue-Hing, Director of Research, Chicago Metro Sanitary
District - Didn't want to talk over the phone. Responded to our letter by
sending us several publications of the district pertaining to the occurrence
and behavior of heavy metals in their system and at their disposal site.
Ross Caballero, Los Angeles - We discussed the use of sludge as
a soil conditioner in California; Kellogg*s (dried sludge) has been used
for 35-40 years with no ill effects. He did observe that, in the past, this
sludge was derived from primary plants with 30-40 percent solids removal;
new plants will remove = 60 percent and expected technology will remove
70 percent. This change in process may effect major changes in sludge pick-
up of toxic metals.
They recently started a project to measure plant pickups using
wastewater for irrigation and sludge used as a soil conditioner. Unfortunately,
the man who was the guiding spirit left and the project has only recently
been reinitiated.
They have data from an upstream treatment facility (as LA is
spread out, with residential areas in the hills, primary treatment facilities
have been constructed partly for hydraulic relief). If the data from this
facility which serves an upper class residential neighborhood are extra-
polated to the city as a whole, they find:
Residential Nonresidential
Percentage Percentage
Cd 17 83
Zn 25 75
Cu 13 87
Cr 2 98
Ni 12 88
Ag 45 55
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50
The silver they interpreted as being an upper class artifact,
the result of photography as a hobby.
They are going to try to get better data as this is necessary
to establish a basis on which to charge for sewage services. They want
to get a good cross-section of the community-industrial, commercial, and
residential with the residential category subdivided according to socio-
economic status. They are trying at the moment to find a method of automatic
sample collection. At the early stage in the sewage system from which they
wish to extract samples, the influent is insufficiently disaggregated to
provide homogeneous samples. They hope to resolve this difficulty in
the next few months.
Larry Klein, New York - He is a bit defensive about the article
he and others published as reaction to it has not been uniformly favorable.
He is very anxious for others to repeat the experiment and is eager for
someone to examine his data and therefore the conclusions. The data
collection is massive.
Dick Field, EPA, Edison, New Jersey - We contacted Mr. Field
regarding data on runoff contributions to metal loading. He sent us a
number of studies most of which measured total street loads. Some idea
of the actual sewer loads could be obtained (see section on street runoff
contributions).
Gr. Cincinnati Sewer District - Discussions with several District
personnel to obtain operating information on treatment plants, mean daily
flow, residential versus industrial nature of influents, and combined
versus separate sewers.
Rufus L. Chaney (USDA) - He has done much work in the area of
plant pickup of toxic metals. He referred us to several publications of
his In this area which he sent to us. He did note that the question of
livestock pickup was completely unexplored. He also observed that the
plant pickup situation involves enougli variables in a sufficiently complicated
way that, an investigator can get any answer he wants, e.g., choice of corn
versus a leaf vegetable would lead to differing conclusions as to the
potential dangers associated with plant pickup.
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51
Ronald Cherry (Atlanta) - They have performed analyses on urban
discharges from various areas near Atlanta. The data are obtained from
receiving streams and there is apparently no way to correlate the weighted
loading or concentration to a particular source.
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52
REFERENCES
(1) Klein, L.D.; Lang, M.; Nash, N.; and Kirschner, S.I. 1974. "Sources
of Metals in New York City Wastewater", Journal WPCF 46 (12): 2653.
(2) Davis, J.A. Ill and Jacknow, J. 1975. "Heavy Metals in Wastewater in
Three Urban Areas", Journal WPCF 47^ (9): 2292.
(3) Benard, and Martin, E.J. 1975. "Part II-Cadmium Loadings on the
Pittsburgh Wastewater Treatment Plant", USEPA Document.
(4) Sanjour, W. 1974. "Cadmium and Environmental Policy" (Draft Document)
USEPA Office of Water and Haz. Materials.
(5) Caballero, R. 1976. Private Communication.
(6) Zenz, D., et al. "USEPA Guidelines on Sludge Utilization and Disposal-
A Review of its Impact Upon Municipal Wastewater Treatment Agencies",
Presented by the MSD of Greater Chicago to the 48th WPCF Conference,
Miami Beach, Florida, October, 1975.
(7) "Draft Development for Proposed Effluent Guidelines and New Source
Performance Standards for the Auto and Other Laundries Point Source
Category" 1974. USEPA.
(8) Breeze, V.G. 1973. "Land Reclamation and River Pollution Problems
in the Croal Valley Caused by Waste from Chromate Manufacture",
J. Applied Ecol. H):513.
(9) Van Loon, J.C., and Lichwa, J. 1973. "A Study of the Atomic Absorption
Determination of Some Important Heavy Metals and Domestic Sewage Plant
Sludges", Environmental Letters 4/1):1.
(10) Fleischer, M. , Sarofim, A. F., Fassett, D. W., Hammond, P., Shacklette,
II. T., Nlsbet, I.C.T., and Epstein, S. 1974. "Environmental Impact of
Cadmium: A Review by the Panel on Hazardous Trace Substances",
Environmental Health Perspectives, p. 253.
(11) Brown, H.G., Hensley, C. P., McKinney, G. L., and Robinson, J. L. 1973.
"Efficiency of Heavy Metals Removal in Municipal Sewage Treatment Plants",
Environmental Letters 5(2):103.
(12) S.'irtor, J. D. , and Boyd, G. B. 1972. "Water Pollution Aspects of Surface
Street Contaminants", EPA-R2-72-081.
(13) Pitt, R. E,, and Amy, G. 1973. "Toxic Materials Analysis of Surface
Street Contaminants", EPA-R2-73-283.
(14) Discussions: 1970. "Lead in Soils and Plants: Its Relationship to
Traffic. Volume and Proximity to Highways" Environmental Science and
Technology 4(3):231.
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53
(15) Lagerwerff, J. V. and Specht, A. W. 1970. "Contamination of Roadside
Soil and Vegetation with Cadmium, Nickel, Lead, and Zinc", Environ-
mental Science and Technology, 4/7):583-586.
(16) Nightengale, Harry I. 1975. "Lead, zinc, and Copper in Soils of Urban
Storm-Runoff Retention Basins", Am. Water Works Assoc. Journal, 67
(8):443.
(17) Korte, N. E., Skopp, J., Niebla, E. E., and Fuller, W. H. 1975. "A
Baseline Study on Trace Metal Election from Diverse Soil Types",
Water, Air, and Soil Pollution, _5_:15°-
(18) Colston, V. 1974. "Characterization and Treatment of Urban Land
Runoff", EPA-670/2-74-096.
(19) McCuen, R. H. 1975. "Flood Runoff from Urban Areas", University of
Maryland, Water Resources Research Center, College Park.
(20) Hergert, S. L. 1972. "Urban Runoff Quality and Modeling Study",
Master's Thesis, Nebraska University, Lincoln.
(21) Salotto, B. V., Grossman, E., III, and Farrell, J. B. 1974. "Elemental
Analysis of Wastewater Sludges from 33 Wastewater Treatment Plants
in the United States", Paper presented at the Research Symposium on
Pretreatment and Ultimate Disposal of Wastewater Solids; published as
EPA 902 (9-74-002).
(22) Nilsson, R. 1971. "Removal of Metals by Chemical Treatment of Municipal
Wastewater", Water Research _5_:51, Pergamon Press.
(23) Furr, A.K., Lawrence, A. W., Tong, S.S.C., Grandolfo, M. C., Hofstader,
R. A., Backe, C. A., Gutenmann, W. H., and Lisk, D. J. 1976. "Multi-
clement and Chlorinated Hydrocarbon Analysis of Municipal Sewage
Sludges of American Cities", Environmental Science and Technology 10
(7):683.
(24) Stumra, W., and Morgan, J. J. 1970. Aquatic Chemistry: An Introduction
Emphasizing Chemical Equilibria in Natural Waters, New York, Wiley,
Interscience.
(25) Roberts, P., Hegl, H., Weber, A., and Krahenbuhl, H. 1975. "Metals
in Municipal Wastewater and Their Elimination in Sewage Treatment",
EAWAG News, Swiss Federal Institute of Technology, Federal Institute
for Water Resources and Water Pollution Control.
(26) Mytelka, A. I., Czachor, J. S., Guggino, W. B., and Golub, H. 1973.
"Heavy Metals in Wastewater and Treatment Plant Effluents", J.W.P.C.F.
45(9):1859.
(27) M.iruyamn, T. , Hannah, S. A., and Column, J. M. 1975. "Metal Removal
l>y Physical and Chemical Treatment Processes", J.W.P.C.F. 47(5):962.
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54
(28) Greater Cincinnati Sewer Districts. 1976. Unpublished data and
personal communication.
(29) Chaney, R. L., "Crop and Food Chain Effects of Toxic Elements in
Sludges and Effluents". Proceedings Joint Conference on Recycling
Sludges and Effluents on Land, National Association State University
and Land Grant Colleges, Washington, C., pp. 129-141.
(30) Garcia, W. J., et al. 1974. "Heavy Metals in Food Products from Corn".
: Cereal Chemistry 51:779.
(31) Fulkerson, W. 1975. "Cadmium - The Dissipated Element Revisited".
2nd National Conference on Water Reuse, AIChE.
(32) Reuss, J., et al., "Plant Uptake of Cd from Phosphate Fertilizer".
To be published.
(33) Haghiri, F. 1973. "Cadmium Uptake by Plants". Journal of Environmental
Quality J2:93.
(34) Chaney, R. L., "Plant Uptake of Heavy Metals from Sewage Sludge
Applied to Land".
(35) Brown, R. E., "The Environmental Significance of Trace Metals and
Nitrates in Sludge Amended Soils". Ohio EPA, to be published.
(36) Garcia, W. J., et al. 1974. "Physical-Chemical Characteristics and
Heavy Metal Content of Corn Grown on Sludge Treated Strip-Mine Soil".
Ag and Food Chem. 22^:810.
(37) Sopper, W. E., et al., "Revegetation of Strip Mine, Spoils Banks
with Municipal Sewage Effluent and Sludge".
(38) Edgerton, B. R., "Revegetating Bituminous Strip Mine Spoils with
Municipal Wastewater. Part I: Grass and Legume Establishment".
(3S[) Pctrasek, A. C. Jr., and Esmond, S. E. 1976. Paper presented at
3rd National Conference on Water Reuse. Al. ChE., Cincinnati.
(40) Seabrook, Belford, L. "Land Application of Wastewater in Australia",
; USEPA Technical Report, EPA-43019-75-017.
(4'1) Hinesly, T. D. , et al. 1976. "Soybean Yield Responses and Assimilation
of Zn and Cd from Sewage Sludge Amended Soil": Journal WPCF, 48(9),
2137.
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