United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/003 Mar 1985
Project Summary
Removal of Heavy Metals Using
Aluminum Salts for
Phosphorus Removal
Donald B. Aulenbach, Nicholas L. Clesceri, Michael A. Meyer,
Chittibabu Vasudevan, Eileen Beckwith, and Shrikant Joshi
A study was conducted to determine
whether the removal of heavy metals
from wastewater would be enhanced if
an aluminum salt was added in a
concentration sufficient to remove
phosphorus. The practice of removing
phosphorus with aluminum salts such
as alum and sodium aluminate is com-
mon to wastewater treatment plants.
The project examined three publicly
owned treatment works (POTWs) in
Massachusetts where sodium aluminate
or alum was used for phosphorus
removal during the summer months.
Samples were taken during the last 30
days of aluminum salt addition in the
fall and during the first 30 days without
it. A statistical analysis was then made
of the impact of aluminum salts on
heavy metal removals. Some 15,000
metal analyses were conducted, and
phosphorus and total organic carbon
(TOC) removals were also measured.
Statistically, the only metal whose
removal was enhanced by the addition
of both aluminum salts was copper.
Sodium aluminate appeared to improve
chromium removal, but alum did not.
Some removal of lead was apparent,
but because of the variation in the
concentrations, this result could not be
confirmed statistically. Phosphorus was
effectively removed by the added alu-
minum. The other metals detected
(silver, arsenic, cadmium, mercury,
antimony, selenium, and zinc) were all
reduced below detectable limits by the
conventional treatment process without
the addition of any aluminum salt.
Beryllium, nickel, and thallium were not
present above detection limits in the
treatment plant influent.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Domestic wastewaters, especially
those containing industrial wastes, may
contain heavy metals in varying degrees.
The removal of these metals (specifically,
the 13 on the priority pollutant list), is of
concern because of the toxic nature of
these metals. Another concern in waste-
water treatment is the removal of phos-
phorus because it is a stimulant to
biological growth in the receiving waters.
Phosphorus removal is required year-
round in publicly owned treatment works
(POTWs) in the Great Lakes basin. In
other locations, phosphorus removal may
be required only during the warmer
months when the element would have a
greater tendency to stimulate algae and
aquatic weed growth.
Aluminum salts such as alum and
sodium aluminate have been commonly
used to remove phosphorus from waste
water. Studies have also shown that
these aluminum salts can remove heavy
metals, but at dosages higher than those
normally used for phosphorus removal.
This study investigates the possibility that
aluminum salt addition in a concentration
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sufficient to remove phosphorus could
also enhance the removal of heavy metals.
Three POTWs in Massachusetts were
studied. Two use sodium aluminate, and
the third uses alum for phosphorus
removal. All three plants are required to
remove phosphorus during the summer
only. Thus the heavy metal removals with
and without the aluminum salt additions
could be compared by sampling for the
last 30 days of aluminum salt addition in
the fall and for the first 30 days after it
was discontinued. All three POTWs were
activated sludge plants treating primarily
domestic waste with a small industrial
input. Some variations occurred in the
design of each plant. One used a trickling
filter before the activated sludge process.
Another plant did not use primary sedi-
mentation but had a final sand filter
following secondary clarification after the
activated sludge treatment. The third
plant had two entirely separate aeration
systems; the system with the longer
aeration time was in operation at the time
of the study.
Procedures
At all three POTWs, daily composite
samples were taken from the influent, the
primary sedimentation effluent where
applicable, and the secondary clarifier
following the activated sludge treatment.
In addition, composite samples were
taken from the sand filter effluent for the
POTW that used no primary sedimenta-
tion. Weekly sludge and supernatant
samples were also secured. Most of the
composite samples were refrigerated, but
because sampling was done in October
and November, refrigeration requirements
were minimal. All samples were trans-
ported under ice to the laboratories at
Rensselaer Polytechnic Institute (RPI)
where the samples were filtered to sepa-
rate the soluble from the particulate
fractions. In addition to aluminum and the
13 metals on the priority pollutant list,
measurements were made for phospho-
rus, TOC, biochemical oxygen demand
(BOD), and suspended solids. These latter
measurements were made to determine
whether the aluminum salt addition
enhanced their removal. Obviously phos-
phorus removal was anticipated.
Except for mercury, the metal analyses
were performed using either a Perkin-
Elmer 303 AtomicSpectrophotometer* in
the graphite furnace mode or a Beckman
Atomic Absorption Spectrophotometer in
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
the flame mode. Mercury was analyzed
by the cold vapor technique. Other
analyses were conducted according to
Standard Methods (StandardMethods for
the Examination of Water and Waste-
water, 15th Edition, APHA, AWWA,
WPCF, 1980).
Because some 15,000 analyses were
conducted, a statistical analysis of the
results was performed. Mean values of
the metal concentrations in the influent,
the intermediate effluent, and the final
effluent were made for both the soluble
and the total fraction and were compared
both with and without the addition of the
aluminum salt. Standard deviations were
also determined. An attempt was made to
correlate the various parameters both
with the addition of the aluminum salt
and with each other. An attempt was also
made to make a mass balance of the
heavy metals in the various portions of
the treatment plant. Because of the
unknown flow rates of the sludge and the
supernatant return, it was not possible to
perform precise mass balances.
In numerous instances, the metal anal-
yses indicated concentrations at or below
the minimum detectable limit. Since it
was not possible to determine how much
they were below the detectable limit, the
values were arbitrarily listed as being
present at the minimum detectable limit,
though many were probably present at
much lower levels. Thus some of the
mean values are probably somewhat high
because of this procedure.
Results
Three metals—thallium, beryllium, and
nickel—were not found at concentrations
above the minimum detectable limit of
the methods used. Therefore no evalua-
tion was made of the impact of the alumi-
num salt addition on the removal of these
heavy metals. Copper, chromium, and to
some extent lead were removed signifi-
cantly. Sodium aluminate addition ap-
peared to improve chromium removal,
but alum had no similar effect. Lead
removal was somewhat obscured by the
large variation in the daily values ob-
tained. Aluminum salt addition appeared
to have no significant impact on antimony
and cadmium removal. The impact of
alum or sodium aluminate addition on the
remaining metals (arsenic, mercury,
selenium, silver, and zinc) could not be
determined. They were removed in the
treatment system without the addition of
the aluminum salt. Though it is good to
know that normal activated sludge treat-
ment is quite effective in removing heavy
metals, information is still lacking on the I
enhancement of their removal by the
aluminum.
Phosphorus removal was definitely
enhanced by adding the aluminum salt,
but TOC removal appeared to be unaf-
fected.
Tables 1, 2, and 3 showthe reduction in
the various metals in the total sample at
each of the three treatment plants. The
overall reductions are shown comparing
the concentrations of the metals in the
influent with those in the final effluent.
Discussion
Even though thallium, beryllium, and
nickel were not found in detectable levels
in the POTW influents, beryllium and
thallium were measured in sludges. Since
the sludges represent a concentration of
materials, it may be assumed that small
amounts of these metals are present in
the influent, though below the detectable
limits. Also, the concentrations of these
metals in the sludges were generally
higher during the period when the alumi-
num salts were added, indicating an
enhancement of removal by the addition
of the aluminum salt.
Silver was found mostly in the particu-
late phase. Little removal occurred in the
primary sedimentation, but the activated
sludge treatment provided significant
silver removal even without the aluminum
salt.
Arsenic was found in only the Pittsf ield
influent, and the removal was nearly
complete in the treatment system without
the addition of the aluminum salt. Thus
no conclusions can be made about the
effect of alum on arsenic removal.
About 25 to 30 percent of the cadmium
was in the soluble phase inthe influentto
the three treatment plants. Primary sedi-
mentation achieved little removal, but the
overall activated sludge system provided
significant removal, again negating any
measureable impact from the addition of
the aluminum salt.
Chromium was present primarily in the
insoluble phase inthe influent to all three
treatment plants. Little removal occurred
during primary treatment, but there was
significant removal in the activated sludge
system. Sodium aluminate addition at
Pittsfield significantly improved the chro-
mium removal.
Total copper concentrations were about
five times the soluble concentrations in
all three POTW influents Little copper
was removed by primary treatment.
Though some measureable removal of
copper occurred in the treatment system
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Table 1 . Mean Removal of Wastewater Constituents in Fitchburg POTW
With Alum Without Alum
Constituent
Aluminum
Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Phosphorus
TOC
Influent Final
Effluent
uo/L
7,823.7 652.8
72.66 77.58
7 05 5 73
0.5*
5.86 0.57
758.8 773
528.9 42.3
767.3 78.2
0.29 0 20*
7,000.*
72.79 70.83
28.79 2.00*
5.0*
550. 300.
mg/L
4.33 0.68
44.09 8.88
% Reduction
54.2
8.5
18.7
903
89.7
92.0
898
37 0+
77.2
93 7 +
45.5+
84.3
79.9
Influent Final
Effluent
ug/L
t*y *-
2,006.4 533 8
75.9 72.36
7.58 7.57
05
7.56 0 92
782.4 78.6
397.8 65.5
872.7 750.0
0.34 0 22
7,000 *
70.75 70.76
23.42 2.46
5.0*
580 300.
mg/L
4.74 2.03
51.01 9.36
% Reduction
73.4
186
0.9
87.8
89.8
83.3
82.8
35.3
5.5
89.5
48.3+
572
87 7
"Minimum detectable limit.
Table 2.
Mean Removal of Wastewater Constituents in Medfield POTW
With Sodium Aluminate
Constituent
Aluminum
Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Phosphorus
TOC
Influent Final
Effluent
H9/L
1,889.8 97.4
14.06 12.39
7 70 5.99
0.5*
7.70 0.80
25.5 3 3
418.3 19 1
85.1 90
1.03 020*
1,000.*
13.53 12 1 1
11.04 200*
50*
970. 300. *
mg/L
5.58 0.59
80.71 6.44
% Reduction
94.8
11.9
222
—
89.6
87.7
95.4
89.4
80.6+
—
70.5
8/. 9+
—
69.7 +
89.4
92.0
Without Sodium Aluminate
Influent Final
Effluent
Ug/L
2,546.0 73.3
73.45 72.73
6.75 6.27
0.5*
4.23 0.50
78.8 5.2
757.5 77.7
62.9 9.3
7.55 0.20*
7,000. *
70.46 70.00*
7.67 2.00*
5.0*
490. 300. *
mg/L
4.18 2.59
46.97 6.95
% Reduction
97.1
5.4
0
—
88.2
72.3
89 7
85.2
87.7
—
4.4+
739+
—
38.8
38.0
85.2
in the primary treatment systems studied.
High overall lead removals were observed
when the aluminum salts were used, but
because of the large variation in the data.
this result could not be confirmed statis-
tically.
A\ bmaii aiiiuuiii ui aniimoriy wdo
detected in all of the POTW influents.
Analyses showed a higher concentration
of antimony following primary treatment
than in the influent. This increase was
attributed either to removal of some inter-
ferring substance in primary treatment or
to the laboratory techniques. The overall
removal of antimony was poor, both with
and without the aluminum salt addition.
Selenium was present in small concen-
trations at Pittsfield, but most of this was
removed by the normal treatment without
the addition of the sodium aluminate.
No soluble zinc was found above the
detection limits in any of the treatment
plants but it must be pointed out that the
1-mg/L detection limit for zinc is rather
high. In the few instances where zinc was
detected, it was all removed by the normal
treatment process without the aluminum
salt addition.
Aluminum measurements were made
to assure that the addition of the alumi-
num salts did not produce an undesirable
aluminum content in the final effluent.
Significant aluminum removal was
achieved both with and without the
aluminum salt addition, thus indicating
that the normal treatment procedures at
these POTWs are adequate for controlling
aluminum in the final effluent.
The activated sludge treatment removed
about 80 percent of the TOC in all cases.
No significant difference occurred in TOC
removal when the aluminum salts were
added.
The addition of the aluminum salts did
significantly reduce the phosphorus con-
tent of each treatment plant effluent. As a
general rule, the phosphorus concentra-
tion in the effluent with the aluminum
salt addition was less than 1 mg/L. Thus
the aluminum salt addition was very
effective in phosphorus removal.
Conclusions
^Minimum detectable limit.
without the aluminum salts, the addition
of the aluminum salts definitely enhanced
the copper removal.
None of the POTWs had other than very
low levels of mercury, all of which were
removed by the primary treatment. Thus
no evaluation could be made of the impact
of the aluminum salt addition on the
mercury removal.
Lead was found in significant concen-
trations in all of the treatment plants,
especially at Fitchburg. The soluble por-
tion was less than 10 percent of the total
lead concentration. Lead removal varied
Statistically, copper was the only metal
whose removal was enhanced by the
addition of both alum and sodium alumi-
nate. Lead appeared to be removed to
some extent, but this result could not be
confirmed statistically because of the
wide variations in influent lead concen-
trations. Sodium alurnmate appeared to
improve chromium removal, but alum did
not. Phosphorus was effectively reduced
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fable 3, Mean Removal of Wastewater Constituents in Pittsfield POTW
With Sodium Aluminate Without Sodium Aluminate
Influent Final % Reduction Influent Final % Reduction
Constituent Effluent Effluent
ug/L fjg/L
Aluminum 23,367. 1,032.1 95.6 13,352. 1,024.9 92.3
Antimony 20.3 11.45 42.8 18.58 13.05 29.8
Arsenic 21.49 7.39 65.6 1528 7.91 48.2
Beryllium 0.5* — — 05*
Cadmium 17.29 4.10 76.3 23.59 4.23 82.2
Chromium 48.1 38 921 58.4 7.0 88.0
Copper 536.1 57.9 89.2 603.8 102.4 83.0
Lead 72.3 5.9 91.8 108.5 28.3 73.9
Mercury 0.64 0.23 64.1 0.52 023 55.8
Nickel 1.000.* — — 1.000.*
Selenium 25.06 16.81 32.9 16.04 10.65 33.6
Silver 20.86 2.00* 30.4 37.97 2.57 32.0
Thallium 5.0* — — 5.0*
Zinc 990 300* 69.7+ 790. 300.* 62.0+
mg/L mg/L
Phosphorus 6.95 1.09 84.3 5.55 2.41 566
TOC 78.30 13.64 82.6 126.19 18.14 85.6
* Minimum detectable limit.
Donald B. Aulenbach, Nicholas L. Clesceri, Michael A. Meyer. Chittibabu
Vasudevan, Eileen Beckwith, and Shrikant Joshi are with Rensselaer
Polytechnic Institute. Troy, NY 12181.
Sidney Hannah and Richard Dobbs are the EPA Project Officers (see below).
The complete report, entitled "Removal of Heavy Metals Using Aluminum Salts
for Phosphorus Removal, "(Order No. PB 85-147 445/AS; Cost: $23.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, V 'A 221 61
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
by the added aluminum salts. Thallium, J
beryllium, and nickel were neverfound in
detectable quantities in the treatment
plant influent. Cadmium and antimony
removals were not significantly affected
by the addition of aluminum salts. The
selenium, silver, and zinc), were all
reduced below the detectable limits by
the conventional treatment process
without the addition of any aluminum
salt. Thus adding aluminum in concentra-
tions designed for effective phosphorus
removal in a POTW can also be effective
to a limited degree in removing certain
heavy metals. For the most part, conven-
tional activated sludge treatment appears
to be effective in reducing the heavy
metal contents of wastewaters.
The full report was submitted in fulfill-
ment of Cooperative Agreement 809226
by Rensselaer Polytechnic Institute under
the sponsorship of the U.S. Environmental
Protection Agency.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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