United States Industrial Environmental Research EPA-600/7-80-052
Environmental Protection Laboratory March 1980
Agency Research Triangle Park NC 27711
Evaluation of Lime
Precipitation for Treating
Boiler Tube Cleaning Wastes
Interagency
Energy/Environment
R&D Program Report
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EPA-600/7-80-052
March 1980
Evaluation of Lime Precipitation
for Treating Boiler Tube
Cleaning Wastes
by
P.J. Rogoshewski and D.D. Carstea
Hittman Associates, Inc.
9190 Red Branch Road
Columbia, Maryland 21045
Contract No. 68-02-2684
Program Element No. INE624A
EPA Project Officer: Julian W. Jones
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460 .
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NOTICE
This report was prepared as an account of work spon-
sored by the United States Environmental Protection Agency
(U.S. EPA). It shall have standing in any EPA proceeding or
court proceeding only to the extent that it represents the
views of the Contractor who studied the subject industries
and prepared the information and recommendations. It cannot
be cited, referenced, or represented in any respect in any
such proceedings as a statement of EPA's views regarding the
subject industries.
2 1
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TABLE OF CONTENTS
Page
NOTICE ii
TABLE OF CONTENTS Hi
LIST OF FIGURES v
LIST OF TABLES vi
ABSTRACT ix
I. INTRODUCTION 1
II. CONCLUSIONS 3
III. RECOMMENDATIONS 4
IV. DESCRIPTION OF BOILER TUBESIDE CHEMICAL CLEANING
SYSTEMS 6
A. Solutions with Metal Chelating and Complex-
ing Properties Used for Boiler Cleaning 6
V. FIELD SAMPLING 15
A. Boiler Tubeside Chemical Cleaning Systems.... 15
B. Boiler Fireside-Air Preheater Wash Waste-
Water Composites 19
VI. EXPERIMENTAL PROCEDURES 22
A. General Procedures 22
B. Analytical Procedures 23
VII. LABORATORY DETERMINATION OF BEST TREATMENT LEVELS
FOR BOILER TUBESIDE CHEMICAL CLEANING WASTEWATER.. 27
A. Initial Analysis of Untreated Wastewater
Samples 27
B. Lime Precipitation Testing 29
C. Lime Precipitation/Polymers Testing 44
D. Optimization Testing of the Ammoniated EDTA
System Wastewater 53
Hi
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TABLE OF CONTENTS (CONTINUED)
Page
E. Statistical Testing 62
F. Sludge Characterization 70
G. Additional Testing of Ammoniated Citric
Acid and Hydroxyacetic-Formic Acid Waste-
waters 84
VIII. APPLICABILITY OF LABORATORY TESTS TO FULL-SCALE
TREATMENT 90
A. Field Conditions 90
B. Process Conditions 94
C. Requirements for Process Equipment and
Materials 97
IX. REFERENCES 99
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LIST OF FIGURES
Number Title
1 Ammoniated Citric Acid System Iron Residual
vs. pH at Four Dilutions with Fireside
Washwater 38
2 Ammoniated Citric Acid System Copper Resid-
ual vs. pH at Four Dilutions with Fireside
Washwater 39
3 Ammoniated Citric Acid System Nickel Resid-
ual vs. pH at Four Dilution Ratios with
Fireside Washwater 40
4 Ammoniated Citric Acid System Zinc Residual
vs. pH at Four Dilutions with Fireside
Washwater 41
5 Ammoniated Citric Acid System Total Sus-
pended Solids vs. pH at Four Dilutions with
Fireside Washwater 42
6 Settling Curve - Run #1 73
7 Settling Curve - Run #2 74
8 Settling Curve - Run #3 75
9 Settling Curve - Run #4 76
10 Settling Curve - Run #5 77
11 Apparatus for Buchner Funnel Test 79
V
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LIST OF TABLES
Number Title Page
1 Stability Constants of Predominant Hydroxya-
cetic and Formic Acid Complexes 13
.2 Stability Constants of Metal-EDTA Complexes.. 14
3 Analysis of Untreated Wastewater Samples 28
4 Lime Precipitation/Dilution of Ammoniated
Bromate/Hydrochloric Acid Boiler Cleaning
Wastewaters 31
5 Lime Precipitation/Dilution of Hydroxy-
acetic-Formic Acid Boiler Cleaning
System Wastewaters 32
6 Lime Precipitation/Dilution of Ammoniated
EDTA Boiler Cleaning System Wastewaters 33
7 Lime Precipitation/Dilution of Thiourea-
HCl/Citric Acid Boiler Cleaning System
Wastewaters 34
8 Lime Precipitation/Dilution of Thiourea-
HC1 Boiler Cleaning System Wastewaters 35
9 Lime Precipitation/Dilution of Ammoniated
Citric Acid Boiler Cleaning System Waste-
waters 36
10 Summary of Best Runs for Lime Precipitation/
Dilution of Six Boiler Cleaning Wastewaters.. 37
11 Preliminary Testing of Polymers with Am-
moniated EDTA Wastewater Composite 45
12 Dilution/Lime Precipitation/Polymer
Addition Treatment of Ammoniated Bromate/
HC1 Boiler Cleaning System Wastewaters 48
13 Dilution/Lime Precipitation/Polymer Ad-
dition Treatment of Thiourea/HCl/Citric
Acid Boiler Cleaning System Wastewaters 48
14 Dilution/Lime Precipitation/Polymer Ad-
dition Treatment of Hydroxyacetic/Formic
Acid Boiler Cleaning System Wastewaters 49
VI
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LIST OF TABLES (CONTINUED)
Number Title
15 Dilution/Lime Precipitation/Polymer Ad-
dition Treatment of Ammoniated EDTA
Boiler Cleaning System Wastewaters 49
16 Dilution/Lime Precipitation/Polymer Ad-
dition Treatment of Ammoniated Citric
Acid Boiler Cleaning System Wastewaters 50
17 Summary of Best Runs for Dilution/Lime
Precipitation/Polymer Addition Testing
of Five Boiler Cleaning Wastewaters 52
18 Summary of Pretreatment Effectiveness for
Ammoniated EDTA System Wastewater 56
19 Optimization of Lime and Diluent Require-
ments 61
20 Homogeneity of Ammoniated EDTA Aliquots 63
21 Statistical Testing of Replicate Treat-
ments 65
22 Results of Student's t-Test on Day-to-
Day Variation 66
23 Mean, Standard Deviation, and Confidence
Interval for Day-to-Day Variation 67
24 Sludge Settling Data 72
25 Sludge Filterability Testing 81
26 Sludge and Filtrate Metal Concentrations 83
27 Analysis of Ammoniated Citric Acid, Hydrox-
yacetic-Formic Acid, and Fireside/Air
Preheater Wash Wastewaters 84
28 Additional Lime Precipitation/Dilution
Testing of Ammoniated Citric Acid System
Boiler Cleaning Wastewaters 86
29 Additional Lime Precipitation/Dilution
Testing of Hydroxyacetic-Formic Acid System
Boiler Cleaning Wastewaters 89
VI1
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LIST OF TABLES (CONTINUED)
Number Title Page
30 Ratio of Available Air Preheater Waste-
water Volume to Chemical Cleaning Waste-
Water Volume 92
31 Characteristics of Coal Pile Drainage 93
32 Summary of Unit Size and Efficiency Changes
Due to 10°C Temperature Increase (20°C to
30°C) 96
VJ.11
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ABSTRACT
This research program was initiated with the overall
objective of exploring the degree of metal removal achiev-
able by lime precipitation treatment of boiler tubeside
cleaning wastes (specifically those which use chelating or
complexing cleaning reagents).
Samples of wastewaters from six boiler tubeside chem-
ical cleanings using complexing and chelating agents were
collected from actual cleanings at power plants. These
samples represented the ammoniacal bromate/hydrochloric
acid, thiourea-hydrochloric acid, hydroxyacetic-formic acid,
ammoniated citric acid, and ammoniated EDTA types of clean-
ing systems. Samples of wastewaters from boiler fireside
and air preheater washes were also collected. A bench-scale
treatment methodology was investigated that involved dilution
of the boiler tubeside wastewaters with a mixture of the
fireside and air preheater wash wastewaters, precipitation
with lime, and addition of polymers to enhance clarifica-
tion. Total and dissolved iron, copper, nickel, zinc, and
total suspended solids were analyzed in the supernatant
after settling. The ammoniated EDTA cleaning system waste-
water was selected as the "most-difficult-to-treat" waste-
water from these data, and was used in subsequent investiga-
tions including the use of various pretreatments and further
adjustments to pH and dilution ratio in an effort to minimize
metal residuals and requirements for lime and diluent.
After determining that a limitation of 1 mg/1 for nickel
could probably not be easily obtained for the ammoniated
EDTA system, additional testing of the ammoniated citric
acid and hydroxyacetic-formic acid wastewaters was also
conducted to minimize pH and lime requirements. A statis-
tical test was conducted to support proper interpretation of
the testing data. Also, the lime sludge from treatment was
investigated for settleability, filterability, and metal
content.
The results indicate that, on a laboratory scale, lime
treatment used in conjunction with dilution by fireside and
air preheater wash wastewaters and addition of polymers is
an effective means of attaining the current effluent guide-
lines limitations that call for 1 mg/1 for iron and copper
in treated wastewaters from boiler tubeside cleanings using
complexing and chelating chemicals. In addition, results of
tests for other metals listed as toxic showed that attainable
zinc residuals ranged from less than 0.01 mg/1 to 1 mg/1.
Attainable nickel residuals were below 1 mg/1 for all systems
other than the ammoniated EDTA, for which the nickel residuals
were not less than 5 mg/1.
2 X
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I. INTRODUCTION
The EPA initiated this investigation to examine lime
treatments as a practical means of removing metals from
boiler tube cleaning wastes. Particular focus was placed on
those wastewaters which contain chelating/complexing
cleaning reagents. The treatment methodology employed in
this investigation consisted of the following:
• Dilution of the boiler tubeside cleaning wastes
with fireside and air preheater wash wastewaters
in order to effect a shift in chemical equilibria,
thereby aiding the precipitation of the subject
metals by lime
• Lime treatment of the diluted wastewater
• The use of polymers to enhance settling and im-
prove clarification.
The first phase of the investigation included the
selection of the predominant boiler tubeside cleaning sys-
tems that use complexing and chelating agents. A descrip-
tion of these systems is presented in Section IV. Waste-
waters from actual boiler cleanings using the selected
systems were then sampled and composited for use in labora-
tory testing. Also, wastewater samples from two fireside/
air preheater washings were collected and composited for use
in the laboratory as diluent. Sampling efforts are
described in greater detail in Section V.
The next phase of the investigation consisted of
laboratory testing using matrices of varying dilution ratios
and pH's, and various polymers with varying dosages. The
main purpose of this phase was to single out a "most-difficult-
to-treat" cleaning system wastewater, which would be used in
further testing to attain effluent guidelines limitations
that would be representative for all subject boiler tubeside
cleaning wastewaters. This phase of the investigation is
detailed in Sections VII-A, B, and C.
The following phase of the investigation consisted of
optimizing the treatment process for the selected most-
difficult-to-treat system wastewater with respect to resi-
dual metal concentrations and lime and diluent requirements.
Further adjustments to pH's and dilution ratios were made
and the effects of a number of pretreatment steps were
investigated. Also, statistical testing to support data
interpretation, and characterization of the resultant lime
sludge were performed. This phase of the investigation is
detailed in Sections VII-D, E, and F.
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In the final phase of investigation, additional labora-
tory testing was conducted on the ammoniated citric acid and
hydroxyacetic-formic acid tubeside cleaning wastewaters.
Further adjustments to pH's and dilution ratios were made in
an effort to minimize lime and diluent requirements for
these two systems. Also, a fireside/air preheater wash
wastewater from a coal-fired boiler was introduced into the
testing, to determine diluent effects on dilution require-
ments, lime requirement, and supernatant metal residuals.
Results of experimentation are presented and discussed
as the experimentation proceeds, in order to provide con-
tinuity and clarity. The overall results of experimentation
as they apply to the feasibility of full-scale treatment are
discussed separately in Section VIII. The experimental
procedures followed in the laboratory to maintain a quality-
controlled testing program are discussed in Section VI.
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II. CONCLUSIONS
The results of laboratory testing program indicate that
lime treatment used in conjunction with dilution by fireside
and air preheater wash wastewaters and addition of polymers
is an effective means of reducing iron and copper in treated
wastewaters from boiler tubeside cleanings using complexing
and chelating chemicals to below 1 mg/1 level.
In addition, zinc residuals in treated wastewaters were
found to be well below 1 mg/1. Nickel residuals no lower
than 5 mg/1 were found to be present in treated wastewater
from the ammoniated EDTA type boiler cleaning; however, for
the other systems tested, nickel residuals below 1 mg/1 were
attainable. Of the 96 Total Suspended Solids analysis
performed 51 exceeded the 30 mg/1 effluent guideline limi-
tation for this class of wastewaters.
Although laboratory testing data indicate that 1 mg/1
of iron and copper is achievable, it is still uncertain
whether the 1 mg/1 level for iron will be attainable in a
full-scale treatment situation. Many of the industry con-
tentions have been evaluated and have been found to be based
on the position that continuous treatment will immediately
follow the wastewater discharges from chemical cleaning.
The treatment methodology under investigation requires that
a large amount of diluent wastewater be stored, and such
storage introduces the feasibility of batch treatment of a
well-mixed raw wastewater with a high degree of flow con-
trol. However, the question remains as to what variability
or loss of efficiency (from poor mixing), if any, will be
introduced by scale-up to full-scale treatment equipment.
There is evidence that some power plants may encounter
difficulties using the specific treatment methodology in-
vestigated under this program; specifically, they may not be
able to generate the required amounts of fireside and air
preheater wash wastewaters for treatment of boiler tubeside
cleaning wastewaters. In these cases, substitute diluents
such as cooling tower blowdown, pond water, or stream water
may be required. It is also recognized that land for
diluent storage may be required for this treatment method-
ology; this land may not be available at some power plants.
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III. RECOMMENDATIONS
A full-scale demonstration of the proposed treatment
methodology under investigation in this study is recom-
mended, so that a proper assessment of any loss of effi-
ciency or variability introduced by scale-up can be made.
It is also recommended that the field demonstration be
conducted on the ammoniated citric acid system which is the
second "most-difficult-to-treat" wastewater. This recom-
mendation stems from another recommendation, which is that
because of the difficulty in removing nickel to levels below
5 mg/1, ammoniated EDTA cleaning wastewaters should not be
treated by the dilution/lime precipitation system studied
under this contract, unless low nickel levels can be guaran-
teed. It should be noted that other boiler cleaning system
wastewaters can also be used for the field evaluation;
however, the data obtained will be less representative of
problems associated with this class of wastewaters.
There was some uncertainty whether supernatant total
iron values of less than 1 mg/1 could be reached when the
fireside/air preheater from the coal-fired boiler was used
as a diluent in the treatment of the ammoniated citric acid
wastewater. Therefore, it is recommended that additional
laboratory testing be conducted between the dilution ratios
of 7:1 and 10:1, and the use of polymers again be investi-
gated.
Because the treatment methodology involves the removal
of metals but not the complexing or chelating agent, more
research should be done on the environmental impact of the
discharge of such contaminants. Some of the organics will
have an effect on BOD and COD. Also, the amount of residual
ammonia in some of the cleaning system treated wastewaters
needs to be determined. Additionally, treatment chemicals
such as inhibitors and passivation agents are known to be
toxic and should be addressed prior to approval of this
treatment methodology. A further investigative recommenda-
tion is a study of metal pick-up rates for each of the
treated wastewaters, to determine any special needs for
nonmetal equipment after clarification and prior to dis-
charge. Finally, a more detailed investigation of metal and
organic constituents in terms of disposal options and environ-
mental considerations is recommended.
Lastly, many water conservation programs have recently
been instituted by the power industry, which are not reflected
by published data. Examples of such water conservation
measures include the use of water recovery and recycle
systems and waterless cleaning of air preheaters (shot
cleaning). Before a final decision is made as to whether
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the technology investigated under this contract be recommend-
ed as practical, a survey of present day diluent wastewater
availability should be initiated, to uncover any changes
induced by water conservation practices that could affect
the feasibility of this treatment scheme.
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IV. DESCRIPTION OF BOILER TUBES IDE
CHEMICAL CLEANING SYSTEMS
A. Solutions with Metal Chelating and
Complexing Properties Used for Boiler Cleaning
The generation of electricity using steam involves the
boiling of water to produce the steam and directing that
steam against blades of a turbine which rotates an electric
generator. Heat, generated during the combustion of fossil
fuels (or by nuclear reactions in nuclear power facilities),
causes steam formation when it is transferred across the
surfaces of boiler tubes, which surround the furnace area,
and into the water which is contained within. Efficient
boiler operation is dependent upon this heat transfer,
therefore much attention is given to the condition of inter-
nal boiler tube surfaces. When deposits form due to the
formation of scale and the accumulation of corrosion products,
impairment of heat transfer results thus lowering efficiency
of the boiler. In addition to the decrease in efficiency,
tube failure may result due to localized overheating. Thus,
chemical cleaning of tube surfaces is required for safety
and economic reasons.
Chemical cleaning of boiler tubesides may be divided
into single and multi-stage processes. These processes may
utilize an acid or alkaline solution to affect dissolution
and complexing of deposited metals. The following principal
cleaning solutions have been found to exhibit metal chelat-
ing or complexing properties:
(1) Hydrochloric acid with copper complexors;
(2) Copper oxidizing and complexing solution used in
conjunction with acid cleaning;
(3) Citric acid based solutions;
(4) Hydroxyacetic/formic acid;
(5) Ammoniated EDTA.
Selection of these five types of cleaning systems was
based on technical data from the two predominant boiler
cleaning service companies, Dow Industrial Service and
Halliburton Services, Inc. (1,2). Although references to
such cleaning agents as sulfuric, sulfonic, gluconic, and
oxalic acids are encountered in the literature (3,4), none
of the available reports of actual cleanings done by power
companies or cleaning services (1,2) confirms use of these
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chemicals. Although each solution is discussed separately,
the following combinations may be employed, resulting in a
multi-stage process:
(1) Any type of chemical cleaning may be preceded by
an alkaline boil-out to remove oil-based compounds
from tube surfaces, if oily substances constitute
a relatively large proportion of the deposit to be
removed. However, the relatively small amounts of
oily substances usually found can be adequately
handled by wetting agents that are often added
during subsequent cleaning stages (5).
(2) Acid cleaning, especially with hydrochloric acid,
may be followed by an alkaline boil-^out and a
subsequent passivation stage. Passivation is
accomplished by circulating or soaking with a
passivating solution such as hydrazine hydrate and
ammonia hydroxide or sodium nitrite (5).
(3) Acid cleaning may be preceded or followed by
copper oxidizing and complexing solutions. Most
commonly employed are ammonium sodium bromate,
ammonium bifluoride, potassium permanganate, and
ammonium persulfate (6,7). Ammonium persulfate is
used less commonly, because of its more hazardous
nature (7). Its primary application is for the
cleaning of the older once-through units with
copper deposition, in which case it is used in
combination with a non-halogenic solvent, such as
hydroxyacetic-formic acid (5). Ammonium bifluor-
ide has also been found to enhance the solubility
of iron deposits and is used commonly.
(4) Cleaning with hydrochloric acid may be followed
with citric acid rinse.
1. Solutions Using Hydrochloric Acid as the Principal
Deposit Dissolver
a. General Description. Hydrochloric acid is a
widely used boiler cleaning agent. It is very effective in
handling a wide range of deposits. Usually, a 5 to 7.5
percent solution of inhibited hydrochloric acid is strong
enough to dissolve most of the mineral and iron parts of
deposits (5). However, the presence of copper warrants
addition of copper complexing agents.
For copper complexing, Dowell Industrial Services
uses straight thiourea while Halliburton has added a pro-
prietary ingredient to their formulation (Cutain II) which
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has been described as a cyclic derivative of thiourea (8).
Characteristics of the two systems are very similar. The
cleaning stage is often followed by a rinse with dilute
citric acid and a passivation stage. Since citric acid is
also a chelating chemical, treatment of wastewaters from a
thiourea/citric acid cleaning may be more difficult.
The advantages of hydrochloric acid as a cleaning
agent are well known (1,2). They include:
(1) Relatively low cost of chemicals involved
(2) Extensive experience accumulated by the
industry
(3) Availability
(4) Compatibility with organic and inorganic
additives. For example, fluoride salts
(ammonium bifluoride) used to solubilize
silicates are highly compatible with hydro-
chloric acid
(5) Availability and wide selection of suitable
inhibitors.
However, several conditions exist which make the
use of hydrochloric acid less desirable as compared with
organic acids and EDTA. Hydrochloric acid is not recommend-
ed for use on once-through boilers since it presents a
significant safety and corrosion hazard (9). Also, cleaning
with hydrochloric acid will generate from five to six boiler
volumes of wastewater, which may pose disposal problems for
the utility.
b. Chemistry of Complexation. Two predominant copper
complexing agents are used in conjunction with hydrochloric
acid cleaning, namely thiourea and Cutain II®. The structure
of thiourea is given below:
H2NCNH2
Thiourea is a strong complexor of the cupric ion, with four
molecules forming coordinate bonds with the copper, as
described below (10):
Cu++ + 4H2NCSNH2 Cu.(H2NCSNH2)4
The stability constant of the complex is cited as 2.5 x 10
(9). Thiourea forms a much weaker complex with zinc, with
8
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the stability constant ranging from 3.16 for the one ligand
complex to 7.94 for the three ligand complex (11). No
information was available on the stability of the iron-
thiourea or nickel-thiourea complex.
Cutain II® is a proprietary formulation of Halli-
burton Services. It consists of a combination of thiourea
and a cyclic derivative of thiourea. No information was
available on the stability of metal complexes formed with
Cutain II®, but one would assume that the stability constant
is similar to that of thiourea. Cutain II® seems to include
chloride as part of the complex, as evidenced by the follow-
ing reaction equations (12).
Iron dioxide dissolution:
Fe304 + 8HC1 + Cutain II®—- FeCl2 + 2FeCl3 +
4H20 + Cutain II®
Copper Complexing:
FeCLo + Cu° + Cutain II®—-FeCl2 +
Cu«Cl»Cutain II
2. Copper Oxidizing and Complexing Solutions Used in a
Separate Stage
a. General Description. These solutions preceed or
follow the acid cleaning stage. Solutions used for copper
removal generally contain free ammonia, ammonium salts, and
an oxidizing agent such as potassium or sodium bromate,
ammonium persulfate, nitrates or nitrites (13). Ammonium
sodium bromate and ammonium persulfate have been used for
the removal of large amounts of copper from boiler deposits
(1,2). Dow Industrial Services uses ammonium sodium bromate
almost exclusively (1) while Halliburton Services use both
(2). However, it appears that the use of ammonium persulf-
ate is not common because of its more hazardous nature (7).
b. Chemistry of Complexation. The active complexing
agent in both ammonium sodium bromate and ammonium persulf-
ate is the ammonia species. Molecular ammonia forms a
strong complex with the cupric ion, with four ammonia mole-
cules forming coordinate bonds with the central copper, as
shown below (10):
Cu++ + 4NH3 - Cu(NH3)4++
This,gositively charged complex has a stability constant of
1x10 at 25°C (14). It is recognized that this complex is
-------
not the only metal-ligand species present, but is predom-
inant. Ammonia also forms moderately strong complexes with
nickel and zinc. The stability constant of the nickel-six
ligand complex is 1.2x10 (25°C) while the predominant
zinc-four ligand complex has a stability constant of
4.47x10 (14). No information was available on iron-ammonia
complexes.
3. Citric Acid Based Solutions
a. General Description. Citric acid has strong
chelating abilities toward the cupric and ferric ion.
Combined with ammonia, it is used to clean moderately dirty
boilers instead of hydrochloric acid with copper complexer.
Because of its low corrosion rate and ease of disposal it
may be preferred over stronger mineral acids.
A process developed by Halliburton Services uses
ammoniated citric acid- for cleaning deposits containing both
iron and copper. This process, Citrosolv®, is a two stage,
one solution procedure. Usually, a 3 percent solution of
citric acid ammoniated to a pH of 3.5 is used as a first
step at temperatures up to 200°F to dissolve iron oxides.
When this reaction is complete the pH is raised to 9 or 10
by the addition of anhydrous ammonia to dissolve copper in
the deposits. The second stage is accompanied by aeration
(15).
The advantages of the Citrosolv® process are cited
as (3,16):
(1) Low corrosion rate
(2) Relatively low toxicity, hence less hazardous
(3) Ease of disposal.
Limitations of the Citrosolv® process include:
(1) Usually not used in boilers with heavy
deposits (2)
(2) Cost of chemicals higher than that of other
acids and cleaning agents (17)
(3) Fluoride salts normally used with other
solvent systems to remove silicates, are not
effective when used with Citrosolv®, hence
there is a necessity to combine the Citrosolv®
process with another treatment if silicates
are present (16). Two stage treatment using
10
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a solution of hydrochloric acid and ammonium
bifluoride in conjunction with the citric
acid stage is recommended for this problem
(16).
b. Chemistry of Complexation. Ammoniated citric acid
has strong complexing capacity towards the ferric and cupric
ions. Citric acid serves to chelate both the cupric and
ferric ions. Its structural formula suggests that it possess-
es very strong chelating ability.
000
ii ii ii
C-OH C-OH C-OH
i i i
CH2 C CH2
OH
The aeration stage, described above, is u.sed to
oxidize ferrous (2 ) iron to the ferric species (3 ), in
order to form the strong ferric-citrate chelate. This-, is
evidenced by a critical stability constant of 3.16x10
(20°C) for the ferric chelate as compared to 2.51x10 for
the ferrous chelate at 20°C (11). There is evidence in the
literature that citric acid may form hydratedocomplexes with
copper with stabilities as high as 1.58 x 10 (18). This
is several orders of magnitude higher than any other metal-
ligand stability constant mentioned in this study. Citric
acid also forms strong hydrated complexes with ionic zinc
and nickel, with stability constants being reported as high
as 2.51 x 10y and 1.66 x 10 , respectively (18).
4. Hydroxyacetic/Formic Acid
a. General Description. Hydroxyacetic/formic acid is
most widely used in cleaning of once-through boilers, where
the use of inorganic acids is prohibitive. The hydroxy-
acetic/formic acid solution chelates iron effectively and in
combination with a corrosion inhibitor and a copper oxidizing/
complexing agent may produce good results in general boiler
cleaning (19,20). Ammonium bifluoride or persulfate is
commonly added in this respect, however, use of a halogen
containing oxidizer precludes use on austenitic steels. A
2:1 mixture of hydroxyacetic/formic acid is usually applied
for cleaning as 3 to 5 percent solution at 200°F (16,20).
The major advantages are cited as (20):
11
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(1) Corrosion protection for bimetallic junctions
(2) Controlled chloride content for austenitic
systems
(3) High iron pick-up
(4) Chelation properties assist in rinse opera-
tion
(5) Minimal corrosive damage from leaks
(6) More effective cleaning due to circulation
(7) Safest method for cleaning once-through
boilers
(8) Generally less costly than citric acid.
b. Chemistry of Complexation. The chemistry of
complexation of hydroxyacetic/formic acid mixtures is not
well known. Roebuck (3) suggests that hydroxyacetic acid is
the main chelating agent. Stability constants taken from
Martell (11) suggest that formic acid may form strong hydrated
complexes with ferric ions; however, this may only occur at
alkaline pH values. Unhydrated complexes for all listed
metal species were found to be relatively weak. An explana-
tion for the strong chelation properties found in operation
is a synergistic contribution of both formic and hydroxyacetic
acids to form a much stronger chelation than the two alone.
This hypothesis has neither appeared nor been verified in
the available literature. The structure of the hydroxyacetic
and formic acid molecules is given below:
HO 0 0
Ml II
H2C-C-OH HC-OH
Hydroxyacetic Acid Formic Acids
Stability constants for complexes of hydroxyacetic
acid and formic acids with various metal ions is given in
Table 1.
12
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TABLE 1. STABILITY CONSTANTS OF PREDOMINANT
HYDROXYACETIC AND FORMIC ACID COMPLEXES (11)
Acid (L)
Formic
Metal ion (M)
CU
2+
Fe
3+
Zn
2+
Hydroxyacetic
Fe2+
Ni2+
CU
2+
Fe
3+
Zn
2+
Equilibrium
[ML]/[M][L]
[ML4]/[M][L]4
[ML]/[M][L]
[M3L6OH2]/[M]3[L]6[OH]2
[ML3]/[M][L3]
[ML]/[M][L]
[ML31/[M][L]3
[ML2]/[M][L]2
[ML3]/[M][L]3
[ML]/[M][L]
[ML2]/[M][L]2
[ML3]/[M][L]3
Log K
0.67 (30°C)
1.9-3.3 (25°C)
3.1 (25°C)
19.9-20.0 (20°C)
1.20
1.33
3.05
3.72-4.66
4.27
2.90
2.92 ± 0.02
3.2 ± 0.3
When ammonium compounds are added to enhance
dissolution and complex formation, the chemistry is similar
to that discussed earlier.
5. Ammoniated EDTA Based Cleaning Solutions
a. General Description. The Alkaline Copper Removal®
Process is based on Vertan 675® chelate. Vertan 675® is a
solution of the tetra-ammoniated salt of ethylenediamine-
tetracetic acid (EDTA) containing organic nitrogen compounds
to inhibit corrosion (21). The cleaning procedure is a
one-solution two-stage process. The first stage consists of
dissolving and chelating iron at pH of 9.0 to 9.5 at tempera-
tures of up to 325°F. After all the iron has been chelated
the temperature is dropped to 188°F and the solution is
oxidized with air. This stage oxidizes the ferrous chelate
to a ferric chelate and it, in turn, oxidizes the copper
into solution and forms a stable cupric chelate. The clean-
ing is complete when the copper concentration levels off
leaving a passivated surface. Among the advantages in using
Vertan® its universality appears to be one of the most
important. Dow claims that Vertan 675® can be used on all
types and sizes of boilers, including austenitic alloys
(3,22).
13
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Low corrosion rate, low volume of wastes (usually
2 boiler volumes), low outage time (2 days) and safety are
the features that may make Vertan 675® an attractive alter-
native to acid cleaning. However, the cost of chemicals
involved may be higher than those for hydrochloric -based
solutions. Vertan 675® is a proprietary formulation and is
not marketed by Dow competitors which limits its share of
the market.
b. Chemistry of Competition. EDTA is one of the most
studied of all chelating agents. It is used in the form of
a tetra-ammoniated salt to increase its solubility and
enhance copper removal. The structure of EDTA is shown as
follows (3).
OH
CH2-C=0
CH9-C=0
2 I
OH
EDTA exhibits very strong chelating properties for
all metal species of concern. It possesses four active
hydronium sites and two addition nitrogen ligands which
suggest that one EDTA molecule may form up to six metal-
ligand bonds with the chelated metal ion. This structural
evidence is confirmed by the stability constants of EDTA
with various metal ion species, as shown in Table 2.
TABLE 2. STABILITY CONSTANTS OF
METAL-EDTA COMPLEXES (23)
Metal ion log K (25°C)
Fe2+ 14.27-14.32
Fe3+ 25.00-25.10
Ni2+ 18.52-18.62
Cu2+ 18.70-18'. 80
Zn2+ 16.44-16.51
14
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V. FIELD SAMPLING
A. Boiler Tubeside Chemical Cleaning Systems
Wastewater samples were collected from six tubeside
chemical cleanings of power plant boilers. These specific
cleanings were chosen to represent the five principal types
of tubeside cleanings presently used in industry, which were
discussed in the previous section. Collected samples were
from the following principal cleaning types.
(1) Ammoniacal bromate/hydrochloric acid
(2) Hydroxyacetic-formic acid
(3) Thiourea-hydrochloric acid
(4) Ammoniated citric acid.
A cleaning using ammonium persulfate was also under
consideration in response to a request by power industry
representatives (5). However, sampling of this additional
cleaning method was not included in the test plan on the
grounds that (1) the copper/ammonia complex is adequately
represented by the ammoniacal bromate system, as well as by
ammonium bifluoride, bicarbonate, ammoniated EDTA, and
ammoniated citric acid; and (2) ammonium persulfate is used
rarely in comparison with ammoniacal broraate, ammonium
bifluoride, and potassium permanganate (6,7).
It should be noted that the optimum sampling approach
would involve collecting samples from several of each type
of boiler cleaning and compositing them to form a representa-
tive sample. However, the financial and time constraints on
the project limited sampling efforts to those described
above. Sample collection of the specific tubeside cleanings
is described in greater detail in the following sections.
1. Ammoniacal Bromate/Hydrochloric Acid
The sample of wastewaters from this type of boiler
cleaning was collected during the cleaning of Unit #2 at the
Tennessee Valley Authority's Gallatin Steam Plant, Gallatin,
Tennessee, on September 12 to 14, 1978. Unit #2 is a Combus-
tion Engineering twin coal-fired furnace, controlled circula-
tion boiler with a holding capacity of 106,000 liters (24).
Cleaning was conducted using a 5 percent inhibited
hydrochloric acid stage and two copper complexing stages,
15
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each consisting of approximately 4 percent potassium bromate
and 6 percent ammonium bicarbonate in solution. These
chemical amounts correspond to the removal of 544 kg of
deposited copper. Hydrazine, rodine, and trisodium phos-
phate were also added during the various cleaning stages.
A total of 10 stages were employed to complete the
cleaning. They are listed below in chronological order:
(a) Hot water flush
(b) Ammoniated bromate stage
(c) First water rinse
(d) Hydrochloric acid stage
(e) Second water rinse
(f) Third water rinse
(g) Second ammoniated bromate stage
(h) Fourth water rinse
(i) Fifth water rinse
(j) Passivation stage.
Following each stage, the boiler was drained for a period of
1-1/4 hours. Samples of approximately 0.5 liter were taken
of each drain every five minutes for a period of one hour.
Composited samples from each drain were further composited
in a 140-liter polyvinyl chloride (PVC) container in order
to represent the total wastewater from the boiler cleaning.
2. Hydroxyacetic-Formic Acid
Wastewater samples from this type of cleaning were col-
lected by Allegheny Power System personnel at the Hatfield
Power Plant, Masontown, Pennsylvania, on October 10 to 12,
1978. The unit cleaned (Unit #1) is a Babcock & Wilcox
supercritical, once-through, coal-fired boiler with a holding
capacity of 261,200 liters (25). It was installed in 1969
and previously cleaned in April 1973.
Cleaning was conducted using a 4 percent solution of
2:1 mixture of hydroxyacetic and formic acids, respectively.
Ammonium bifluoride was also added as a copper complexor.
This stage was followed by two plant feedwater rinse stages
and a final passivation using ammonia and hydrazine. Thus,
a total of four stages were required for cleaning, as sum-
marized below:
(a) Hydroxyacetic-formic acid stage
(b) First water rinse
16
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(c) Second water rinse
(d) Passivation stage.
Two flow-proportional drain samples (114 liters each)
were composited from samples taken every five minutes over
an hour's time. One of the composite samples was taken
during acid circulation and the other was taken during
passivation. The composited samples do not contain the two
rinse stage drainings and so the combined sample used in
testing is approximately twice the concentration of the
total actual wastewater from this cleaning.
3. Ammoniated EDTA
The wastewater sample from this type of cleaning was
collected during the cleaning of Unit #1 at the Dickerson
Power Generating Station, Dickerson, Maryland, on December
11 to 15, 1978. Unit #1 is a Combustion Engineering con-
trolled circulation coal-fired boiler rated at 190 MW with a
holding capacity of 106,000 liters (26).
The boiler cleaning was conducted using an 8.3 percent
solution of ammoniated EDTA with a reported 91 to 136 kg of
copper removed from the boiler (26). Two rinses with seal
water were employed followed by a passivation stage using
hydrazine. The stages used in the cleaning are listed
below:
(a) Ammoniated EDTA stage
(b) First water rinse
(c) Second water rinse
(d) Passivation stage.
Grab samples of the four stages (38 liters each) were
taken directly from the circulation pump after at least one
hour of circulation, insuring representativeness. A defi-
cient volume of sample (11 liters) was collected during the
second rinse, and was therefore not used to make up the
composite. However, passivation is not usually conducted
after ammoniated EDTA cleanings, thus suggesting that a
three-stage cleaning process is probably more common. The
combined sample to be used in initial laboratory testing
(with the second rinse omitted) is expected to have only
slightly different metal concentrations than the total
wastewater from a three-stage cleaning without passivation.
17
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4. Thiourea-Hydrochloric Acid
Two samples of thiourea-hydrochloric acid cleaning
wastewaters were collected for laboratory testing. The
first wastewater sample was collected during the cleaning of
Unit #4 boiler at Florida Power and Light Company's Fort
Lauderdale Power Plant on December 13 to 15, 1978. Boiler
#4 is a Babcock & Wilcox single-drum natural circulation
reheat type oil-fired unit with a holding capacity of 113,562
liters (27). The cleaning solution was composed of approxi-
mately 1 percent thiourea (Cutain II )y 5 percent hydrochloric
acid, 0.2 percent ammonium bifluoride, and 0.2 percent
inhibitor. The cleaning stage was followed by a water rinse
and a second rinse consisting of 0.1 percent citric acid.
Passivation was conducted using a soda ash boil-out. The
stages used in cleaning are listed below:
(a) Thiourea-acid stage
(b) Water rinse
(c) Citric acid rinse
(d) Passivation stage.
Samples of the wastewaters from each of the four stages were
collected continuously during the 1-1/2 hour drain period
and composited in a 114-liter PVC container before shipment
to the laboratory.
A second sample of a thiourea-hydrochloric acid boiler
cleaning was collected at Baltimore Gas & Electric Co.'s
Riverside Power Station, Turners Station, Maryland, on
January 3, 1978. The cleaning was conducted on Boiler #4,
which is a Babcock & Wilcox natural circulation drum-type
oil-fired boiler with a holding capacity of 98,420 liters
(28). The cleaning was conducted using an acid-thiourea
(Cutain II)®stage consisting of about 5 percent hydrochloric
acid, 0.4 percent Cutain III®0.2 percent ammonium bifluoride
and 0.2 percent inhibitor. The cleaning stage was followed
by two water rinses and a soda ash boil-out for passivation.
A total of four stages were required for cleaning, as listed
below:
(a) Thiourea-acid stage
(b) First water rinse
(c) Second water rinse
18
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(d) Passivation stage.
Composite samples of each of the four stages were taken
every six minutes over a period of 1-1/4 hours. The com-
posited samples of each stage were further composited in a
114-liter PVC container before shipment back to the labora-
tory. This second sample of the thiourea-type cleaning
differs from the first in that no citric acid was used in
the rinse.
5. Ammoniated Citric Acid
The samples of wastewaters from the ammoniated citric
acid method were collected by Orange & Rockland Utilities
personnel at the Lovett Power Plant, Tomkins Cove, New York,
on February 16, 1979. The cleaning was conducted on Boiler
#3, which is a Combustion Engineering natural circulation,
tangentially fired, single-drum coal-fired boiler with a
holding capacity of 51,100 liters (29).
A 5 percent solution of citric acid was used in the
cleaning stage, which also contained approximately 0.4
percent ammonium bifluoride, and 0.8 percent sodium nitrite.
The solution pH was raised to 9.5 by addition of 4,220
liters of aqua ammonia and 227 kg of ammonium bicarbonate,
corresponding to concentrations of approximately 2.4 percent
and 0.4 percent, respectively. The cleaning stage was
followed by a first rinse with city water and a second with
high-purity condensate water. Thus, a total of three stages
were required for cleaning, as listed below:
(a) Citric acid rinse
(b) First water rinse
(c) Second water rinse.
A total of 38 liters of sample was taken during the
draining of each stage, with a 3.8-liter volume being col-
lected every 5 to 6 minutes over a period of one hour.
Samples were contained in 3.8-liter glass jugs and picked up
by Hittman personnel for transfer to the laboratory.
B. Boiler Fireside Air Preheater Wash
Vastewater Composites
The washing of boiler firesides and air preheaters is
conducted periodically to remove ash, slag, and soot deposits
from heat exchange surfaces. These deposits accumulate as a
19
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normal result of fuel combustion, and must be removed periodi-
cally to maintain efficient heat transfer in the boiler.
Samples of boiler fireside and air preheater wash
wastewaters were collected for use in the laboratry testing
scheme. These wastewaters were combined before use in the
ratio of 2:1 air preheater wash volume to fireside wash
volume. This ratio was based on relative generated volumes
calculated from the frequency and batch volumes of the two
types of cleanings (30) with the assumption that full scale
treatment could well require collection and storage for a
one-year period.
Two boiler fireside/air preheater wash wastewater
composites were collected for this study.
The first of these composites was collected during the
cleaning of Unit #4 at Baltimore Gas & Electric Company's
Riverside Plant, on October 7 to 8, 1978. Unit #4 is a
Babcock & Wilcox natural circulation drum-type boiler. This
particular power plant uses predominantly #6 fuel oil which
is believed to be extremely high in nickel, since analysis
of the fly ash from this plant yielded a nickel concentra-
tion of 35,000 ppm (31). Thus, wastewaters from the fire-
side and air preheater washings of the boilers in this plant
are expected to contain higher-than-normal concentrations of
nickel.
The fireside cleaning was conducted with a high-pres-
sure stream of water containing a surfactant to aid deposit
breakup. BG&E personnel worked inside the boiler directing
the high-pressure hose toward the fireside surface deposits.
Wastewater from the cleaning trickled down to the sluice
box, where samples were collected. The cleaning was done in
shifts with approximately a 15-liter grab sample taken
during each cleaning shift, corresponding to a total of
76-liters taken at the end of five cleaning shifts.
After cleaning of the fireside tube surfaces, automatic
water jets inside the air preheaters were activated and ran
continuously for approximately six hours. The wastewater
from the cleaning drained into a sluiceway, where it was
collected with a weir and small pump. Four 38-liter grab
samples were collected at 1-1/2 hour intervals, resulting in
a total of 150 liters of samples. Prior to testing, the two
samples were composited in the abovementioned 2:1 ratio in
the laboratory in a 230-liter polyethylene-lined drum.
The above composite sample was used during most of the
laboratory testing.
20
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A second boiler fireside/air preheater wash wastewater
composite sample was collected during the latter stages of
this study for the purposes of assessing dilution require-
ments when lower nickel concentrations were present. The
second set of samples was collected during the cleaning of
Unit #1 at Florida Power Corporation's Crystal River Plant
November 8 to 11, 1979. Unit #1 is a Combustion Engineering
tangentially fired boiler modified for coal burning (32).
The fuel to this unit is a combination of high and low-sulfur
coals from Illinois (Burnside Mine) and Eastern Kentucky
(Coal Resources), respectively, and it was expected that
nickel values would be relatively low as compared to levels
in fuel oil.
Florida Power personnel conducted the fireside washing
using a high-pressure water stream directed toward the
surface deposits. Wastewater from the cleaning flowed into
the sluice box with the overflow being collected in a cylin-
drical tank. Samples of the wastewater were collected from
a tap at the bottom of the overflow tank. The cleaning was
conducted intermittently over a number of shifts for a total
washing time of approximately 12 hours. A 2-liter grab
sample was taken every 15 minutes during a period of wash-
ing, corresponding to a total of 48 liters taken for the
total fireside wash operation. Nineteen liters of this
sample were shipped back to the laboratory.
After the fireside washing was completed, automatic
water jets inside the air preheaters were activated and ran
continuously for approximately 8 hours. The wastewater from
preheater cleaning drained to a sluiceway thence to a wet-
well, where samples were collected. A 2-liter grab sample
was collected every 15 minutes for a total sample of 32
liters. Nineteen liters of this sample were shipped back to
the laboratory.
A 2:1 preheater/fireside wash wastewater composite was
prepared on an as-needed basis from these two samples for
testing during the latter stages of this study.
21
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VI. EXPERIMENTAL PROCEDURES
A. General Procedures
1. Storage of Samples
All boiler tubeside chemical cleaning wastewater samples
were stored at ambient temperature in 19-liter polyethylene
containers. The fireside/air preheater composite was stored
in a 230-liter polyethylene-lined drum, also at ambient
temperature. Because of the highly toxic nature of the
wastewaters, biodegradation of samples is expected to be
minimal during the period of investigation.
2. Sample Mixing
All samples were well mixed while compositing and
taking aliquots and prior to transfer. Small volumes of
samples were shaken vigorously by hand. Volumes of 7 to 20
liters were mixed with a propeller-type mixer. Larger
volumes from 20 to 230 liters were mixed by circulation for
5 to 10 minutes using a 62 W (1/12 HP) centrifugal pump with
an outlet pressure of 15 mPa and a measured flow rate of 18
liters per minute. The pump method was used extensively in
the field and the laboratory to mix and transfer samples.
3. Supernatant Decanting
Supernatants were decanted by using a suction tube with
a side outlet about 13 cm above the end of the tube. A
Nalgene hand pump was used to provide necessary light suc-
tion. Decanted samples were aspirated into a sidearm flask.
After every aspiration, the apparatus was rinsed several
times with deionized water to prevent contamination from
sample to sample. Aspirated samples were placed in acid-
washed holding jars for storage until preparation for analy-
sis .
4. Preparation of Polymer Solutions
Polymer solutions were prepared in accordance with
manufacturer's directions. An automatic pipettor with
disposable tips was used to make up stock and working solu-
tions of polymers. Fresh stock and working solutions were
made up daily, weekly, or monthly, depending on the shelf
life of polymer solutions recommended by the manufacturer.
22
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5. Acid-Washing of Laboratory Apparatus
All laboratory apparatus that had direct contact with
the samples was acid-washed with 1:1 hydrochloric acid prior
to use to prevent metal contamination. The Phipps and Bird
stirrer paddles were washed with a dilute hydrochloric acid
solution.
6. Quality Assurance
In the absence of an absolute reference for research
materials, accuracy and precision must be estimated from
data collected from the actual samples. This is most econo-
mically performed by using spiked samples (for accuracy) and
by determining the values of some samples more than once
(for precision). In the current study, aliquots of at least
10 percent of the samples were spiked with a known amount of
the metal being analyzed or were determined in duplicate.
In addition, 10 percent of the samples were determined in
duplicate. These data showed that the accuracy and pre-
cision of the experimental technique should not prevent
valid data interpretation.
B. Analytical Procedures
1. Total Suspended Solids-Preparation and Analysis
The procedure followed for preparation and analysis for
total suspended solids is described as follows:
(a) Glass-fiber filters with 0.14 pm pore size were
washed in distilled, deionized water. After
successive cleanings, the filters were dried for
one hour at 104°C and removed and placed in a
desiccator to cool.
(b) The filters were then tared and placed in marked
aluminum weighing tins.
(c) An all-glass Millipore Filtration Apparatus was
used. The filtration apparatus was washed with
1:1 HC1 to remove residue, then rinsed with dis-
tilled, deionized water.
(d) Each sample was vigorously shaken for one minute
and then measured in a graduated cylinder to 50 ml
or 100 ml, depending on available supernatant.
23
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(e) A tared filter was placed in the filtration ap-
paratus and the sample was poured in. The graduated
cylinder was rinsed with distilled, deionized
water and this rinse was poured into the apparatus.
Walls of the apparatus were washed down to release
all particles. The filtrate was collected in a
400-ml beaker and discarded.
(f) After filtering, the filter and filter cake were
removed and placed in a marked aluminum weighing
dish and dried in an oven for one hour at 104°C.
The filtration apparatus was thoroughly rinsed
with distilled, deionized water and set up for the
next filtration.
(g) After all samples were filtered and dried in the
dessicator, the filters were weighed, the tare
weight was subtracted, and the appropriate factor
was applied.
(h) Two blanks were analyzed. One hundred milliliters
of distilled, deionized water was filtered through
clean, weighed filters and dried in the oven as
previously stated. Any weight found after drying
and dessication was subtracted from the weights of
the samples.
(i) Three or four duplicate samples were prepared as
previously stated and used as a check on previous
results.
2. Preparation of Samples for Total and Dissolved Metal
Analysis
The procedures followed for preparation of samples for
metals analysis are as follows:
Samples were shaken vigorously for one minute and 50 ml
of sample was used for both filtered and digested analysis.
(a) Filtered Samples (dissolved metals). A 50-ml
sample was filtered through Gelman glass-fiber
filters and the filtrate was caught in a 150-ml
beaker and transferred to an acid-washed boiling
jar. The sample was acidified with 1:1 HNCU (250
ul). These samples were labeled with the assign-
ment number and were ready for analysis.
(b) Digested Samples (total metals). 600-ml beakers
were acid washed with 1:1 HC1 and rinsed with
24
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distilled, deionized water. Fifty milliliters of
homogenous samples were placed into the beaker
with 15 ml of high purity, concentrated HNCs. The
beaker was placed on a hot plate and allowed to
fume but not boil.
(1) After complete drying, 5 to 10 ml of concen-
trated HNO^ was added and a watch glass was
placed over the beaker. The beaker was
placed on a hot plate and allowed to fume but
not boil. Sample was evaporated to dryness.
(2) Five to 10 ml of 1:1 HC1 were added and the
watch glass and beaker were replaced on the
hot plate. Evolution of brown-orange gas
occurred. After the sample had finished
gassing, distilled, deionized water was added
to the beaker and heated until the salt of
the metals was dissolved. Care was taken not
to add more than 50 ml of water.
(3) These samples were filtered through Gelman
glass-fiber filters, stored in acid-washed
bottles, labeled with the assignment number,
and stored until analysis. Samples were
diluted to 50 ml with distilled, deionized
water.
(4) Duplicate blanks were prepared in the same
manner.
3. Analysis of Metals
Analysis of total and dissolved iron, copper, nickel,
and zinc in each sample was performed on a Perkin-Elmer 603
Atomic Absorption Spectrophotometer with Deuterium Arc
Background Correction. Procedures followed are described
below:
(a) Standards were prepared by serial dilutions of
Fisher 1000 ppm Atomic Absorption standards.
Lamps used were Perkin-Elmer Hollow Cathode Lamps
or Electrodeless Lamps.
(b) 10-ml injections were used. An adjustable auto-
matic pipet was used to deliver the sample.
(c) Background correction was used on all analysis.
(d) The blanks were analyzed first to establish the
impurity level of the water.
25
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(e) After all the samples were analyzed, duplicates
and spiked samples were analyzed for quality
control measures.
(f) Acquiring final values was accomplished by linear
regression analysis. The standards and the cor-
responding absorbances are entered into the memory
and a correlation coefficient is obtained. The
absorbances acquired from the samples are auto-
matically plotted on the standard line and the
actual ppm or ppb reading is displayed. The blank
value is then subtracted from the sample value.
26
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VII. LABORATORY DETERMINATION OF BEST TREATMENT
LEVELS FOR BOILER TUBESIDE CHEMICAL
CLEANING WASTEWATERS
Laboratory testing to determine the best treatment
levels for the boiler tubeside chemical cleaning wastewaters
is detailed in the following sections. Under each distinct
experiment, the procedure is presented, followed by the
actual data, and a discussion of the results. In brief,
testing began with an analysis of iron, nickel, copper, and
zinc concentrations in the six chemical cleaning wastewaters
and the fireside/air preheater wash wastewater composit from
the oil-fired boiler. Then, matrix testing of the six
boiler chemical cleaning wastewaters was conducted in which
treatment involving various dilutions with a fireside/air
preheater wash wastewater and lime addition to various pH's
was investigated. Polymers were then introduced to enhance
treatment and matrix testing using different polymers at
different dosages was conducted on the best runs found from
previous testing. From the results of treatment with poly-
mers, a "most difficult to treat" boiler cleaning system
wastewater was then selected. A number of pretreatment
methods were then investigated in an effort to enhance metal
removal efficiencies from the "most difficult to treat"
wastewater. Also, an additional matrix test was performed
in an effort to minimize the lime and diluent requirements
for treatment. A statistical test was then conducted to
support proper interpretation of results. The sludge from
this treatment was characterized with respect to settle-
ability, filterability, and metal content.
Latter stages of experimentation included testing of
the two next "most difficult to treat" chemical cleaning
wastewaters. Various dilutions were prepared with a newly
collected fireside/air preheater wash composite from a
coal-fired boiler. Lime was again added to the dilutions at
various pH's for determination of metal removal.
A. Initial Analysis of Untreated Vastewater Samples
The composited chemical cleaning system wastewaters and
the fireside/air preheater wash wastewater (oil-fired unit)
were analyzed for concentrations of the four metals and for
total suspended solids. Results of analysis are presented
in Table 3.
It is noted that the hydroxyacetic-formic acid waste-
water composite is about twice as concentrated as would be
expected, since the two water rinse samples were omitted.
Also, the ammoniated EDTA wastewater composite would be
27
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TABLE 3. ANALYSIS OF UNTREATED WASTEWATER SAMPLES
(Values Reported in mg/1)
Type of Wastewater
Metals
Fe
Cu
Ni
Zn
TSS
Ammoniated Bromate-
Hydrochloric Acid
Hydroxyacetic-Formic
Acid
Ammoniated EDTA
Thiourea-Hydrochloric
Acid with Citric Rinse
Thiourea-Hydrochloric
Acid
Ammoniated Citric Acid
Fireside/Air Preheater
Wash Composite
(oil-fired)
Total
Total
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
500 110
27
5000
2200
1900
680
660
1500
1400
2000
1600
0.6
Total 4113
Dissolved** 3009
330
330
210
86
31
31
95
95
13
12
74
43
72
83
7
7
30
26
510
195
25
0.2
11
10
15
15
15
14
5
4
21
20
1400
88
147
38
16
98
63190
* Four-run average,
**Two-run average.
# Four-run average.
slightly different in concentration from a standard three-
stage cleaning of the same type, since the second water
rinse sample was omitted and the optional passivation stage
drain sample was substituted. These differences should not
significantly impact the testing program.
Also, it was noted earlier that the fireside/air pre-
heater wash composite was expected to be high in nickel, and
this is confirmed in Table 3. Similar wastewaters from
steam generating units burning oils from other sources or
coal are expected to have much lower concentrations of
nickel. Analysis of a fireside/air preheater wash waste-
water from a coal-fired unit is presented in Section VII-G,
in which nickel levels are substantially lower as expected.
28
-------
B. Lime Precipitation Testing
Lime precipitation testing was conducted on six boiler
tubeside chemical cleaning wastewater samples collected for
this treatability study. The wastewaters correspond to the
following types of cleanings:
(1) Ammoniated bromate/hydrochloric acid
(2) Hydroxyacetic-formic acid
(3) Ammoniated EDTA
(4) Thiourea-hydrochloric acid (2 samples collected)
(5) Ammoniated citric acid
The tubeside chemical cleaning wastewater samples were
tested using various dilutions with fireside/air preheater
wash wastewater. Testing for each sample consisted of
adding lime to attain four pH's, i.e., 8.5, 9.5, 10.5, and
12.0. When some of the chemical cleaning wastewaters were
initially alkaline, such as was the case with the ammoniated
EDTA and citric acid systems, the pH was extended to 13.0
and/or the pH's lower than or equal to the initial pH of the
wastewater were not used. The dilutions of fireside/air
preheater wastewater to chemical cleaning wastewater were
0:1, 1:1, 3:1, and 10:1. Altogether, 16 runs of pH/dilution
combinations (excluding quality control) were conducted for
each of the six samples. After addition of lime to proper
pH, the samples were allowed to settle for 24 hours and the
supernatant was decanted as described under General Pro-
cedures .
After settling, supernatants were analyzed for total
and dissolved iron, copper, nickel, and zinc, and total
suspended solids. Also analyzed were the chemical cleaning
samples before pH adjustment and dilution (total iron,
copper, nickel, and zinc) and the fireside/air preheater
wastewater composite (total and dissolved of above metals).
To adjust pH, straight hydrated lime was slowly fed to the
wastewater mixtures, while they were being stirred at 100
rpm by a Phipps and Bird Laboratory stirrer. The lime was
added by teaspoon and after every addition, the lime was
allowed to react for 5 to 10 minutes before a pH reading was
taken with a pH meter. Smaller and smaller additions of
lime were made until the desired pH was attained. The lime
used in the study was a high calcium hydrated agricultural
grade manufactured by J.W. Barrick & Sons, Woodsboro, Maryland,
with an assay,of 62 percent as CaO and 3 percent as MgO.
29
-------
Results of the testing of the six chemical cleaning
wastewaters at varying pH and dilutions with fireside/air
preheater wash wastewaters are presented in Tables 4 through
10. Tables 4 through 9 present total and dissolved iron,
copper, nickel, and zinc and total suspended solids for
supernatants after 24 hours of settling. As can be seen
from Figures 1 through 5 (ammoniated citric acid wastewater),
the general trend is that supernatant metal residuals de-
crease as the pH and dilution ratio increase. Supernatant
total suspended solids seemed to show a general downward
trend with respect to pH and dilution increases. At the 0:1
dilution, however, this trend was not apparent. Slight
differences in trends can be observed for each of the boiler
cleaning wastewaters.
The ammoniated bromate/hydrochloric acid wastewater
seemed to follow the general trend for copper, nickel, and
zinc. It was observed that the supernatant total iron
residual at pH 8.5 did increase at dilutions of 3:1 and
10:1. If it is statistically significant, this increase
could be due to the contribution of iron from the diluent
(fireside/air preheater wash wastewater). In general, the
metal residuals were moderately low and dropped off quickly
to levels of less than 1 mg/1 starting at a dilution of 3:1
and a pH of 10.5. This system appears to be easiest to
treat of all the wastewaters.
The hydroxyacetic-formic acid wastewater seemed to com-
plex metals introduced by the diluent, as it was observed
that copper and nickel residuals increased upon dilution to
1:1 and 3:1. This increase was noticeable at all pH's for
copper and only at pH's 8.5 and 9.5 for nickel. Iron seemed
to follow the general trend while zinc was almost a consis-
tent 0.1-0.2 mg/1. Metal residuals below 1 mg/1 were reached
at a 10:1 dilution and a pH of 10.5 for all species.
The ammoniated EDTA wastewater did not follow the
general trend. In all metals except copper, residuals first
increased with a dilution to 1:1, then decreased upon further
dilution. The general trend for pH at any specific dilution
(except 0:1) was followed for all metals. It is obvious
that this wastewater has strong chelating properties, and is
chelating metals introduced by the diluent. Extremely high
nickel residuals persisted even at the highest pH and dilution
30
-------
TABLE 4. LIME PRECIPITATION/DILUTION OF AMMONIATED
BROMATE/HYDROCHLORIC ACID BOILER CLEANING WASTEWATERS
(Values reported in mg/1)
Dilution
0:1
0:1
0:1
0:1
1:1
1:1
1:1
1:1
3:1
3:1
3:1
3:1
10:1
10:1
10:1
10:1
£H
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
0.6
<0. 1
0.3
0.1
0.3
0.1
0.3
0.1
0.3
0.1
0.4
0.1
0.3
0.1
0.3
0.1
1.3
0.2
0.6
0.2
0.2
0.1
0.2
0.1
1.9
0.3
0.6
0.2
0.3
0.1
0.3
0.1
Cu
29.7
29.0
37.4
33.4
15.7
15.4
2.8
1.5
1.1
1.3
1.6
1.5
0.5
0.5
0.3
0.2
0.6
0.4
0.6
0.6
0.5
0.5
0.2
0.2
0.2
0.2
0.3
0.2
0.1
0.1
0.1
0.1
Ni
17
17
19
20
8.0
8.0
0.3
0.2
4.2
4.5
2.5
2.6
0.3
0.3
0.2
0.2
2.7
3.0
1.6
1.6
0.3
0.2
0.2
0.1
1.8
1.7
0.5
0.4
0.3
0.2
0.3
0.2
Zn
2.0
0.5
2.4
2.7
1.2
0.9
0.5
0.4
0.3
0.1
0.3
0.1
0.4
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
TSS
0
0
24
115
90
95
37
45
27
36
4
0
49
*
15
26
*Insufficient amount of supernatant available for TSS.
31
-------
TABLE 5. LIME PRECIPITATION/DILUTION OF HYDROXYACETIC-
FORMIC ACID BOILER CLEANING SYSTEM WASTEWATERS
(Values reported in mg/1)
Dilution
0:1
0:1
0:1
0:1
1:1
1:1
1:1
1:1
3:1
3:1
3:1
3:1
10:1
10:1
10:1
10:1
2H
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
460.0
480.0
3.8
3.4
1.7
1.1
2.8
2.0
16.1
11.5
3.0
2.6
0.5
0.2
0.8
0.3
14.2
9.8
1.2
0.3
0.7
0.1
1.2
0.1
1.3
0.1
0.8
0.1
0.5
<0.1
1.0
<0.1
Cu
0.4
0.4
0.3
0.3
0.3
0.2
0.3
0.2
2.4
2.5
2.4
2.5
2.4
2.7
2.3
2.2
1.0
0.8
1.2
0.9
1.0
0.7
1.0
0.9
0.4
0.2
0.4
0.3
0.5
0.3
0.5
0.2
Ni
2.9
2.8
1.3
1.4
0.3
0.4
0.3
0.3
10.6
10.5
2.6
2.8
0.4
0.4
0.2
0.2
9.7
9.8
1.1
1.1
0.2
0.1
0.2
0.1
0.8
0.8
0.3
0.3
0.1
0.1
0.1
0.2
Zn
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.1
0.1
0.3
0.1
0.2
0.1
TSS
20
12
4
27
10
16
14
14
92
28
20
18
22
31
23
16
32
-------
TABLE 6. LIME PRECIPITATION/DILUTION OF AMMONIATED
EDTA BOILER CLEANING SYSTEM WASTEWATERS
(Values reported in mg/1)
Dilution pH
0:1
0:1
0:1
1:1
1:1
1:1
1:1
3:1
3:1
3:1
3:1
10:1
10:1
10:1
10:1
10.5
12.0
13.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
3.0
0.2
12.0
5.0
7.3
2.6
629.0
584.0
308.0
127.0
28.0
0.2
1.1
0.1
492.0
357.0
446.0
243.0
87.0
17.0
1.6
0.1
119.0
95.0
46.0
33.0
77.0
3.5
0.5
0.1
Cu
333.0
329.0
283.0
227. 0
177.0
125.0
116.0
114.0
80.0
83.0
3.0
3.3
0.4
0.4
5.8
5.5
0.6
0.6
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
Ni
47.0
48.0
45.0
45.0
47.0
47.0
189.0
155.0
165.0
156.0
141.0
119.0
100.0
97.0
87.0
81.0
68.0
59.0
51.0
48.0
36.0
39.0
26.0
26.0
15.0
13.0
10.0
9.5
6.8
5.5
Zn
2.3
2.2
0.8
0.7
0.9
0.8
12.0
12.0
8.0
8.0
0.2
0.2
0.1
0.1
8.6
7.9
7.5
6.4
0.1
0.1
0.1
0.1
5.2
5.0
3.2
2.7
0.2
0.1
0.2
<0. 1
TSS
42
212
56
330
798
100
17
230
633
445
24
82
114
310
22
33
-------
TABLE 7. LIME PRECIPITATION/DILUTION OF THIOUREA-HCL
(CITRIC ACID RINSE) BOILER CLEANING SYSTEM WASTEWATERS
(Values reorted in mg/1)
Dilution
0:1
0:1
0:1
0:1
1:1
1:1
1:1
1:1
3:1
3:1
3:1
3:1
10:1
10:1
10:1
10:1
2M
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
1.4
0.2
3.3
0.3
1.6
0.4
2.4
0.2
1.7
0.7
0.5
0.1
0.3
0.1
0.4
0.1
1.4
0.1
0.5
0.1
0.3
0.1
0.4
0.1
1.1
0.3
0.8
0.1
0.6
0.1
1.4
0.1
Cu
25.3
24.6
4.7
4.0
6.8
6.3
0.7
0.8
0.9
0.9
0.7
0.6
0.6
0.4
0.5
0.5
0.5
0.4
0.4
0.4
0.3
0.2
0.2
0.1
0.4
0.2
0.3
0.2
0.4
0.2
1.5
0.2
Ni
1.7
1.4
0.9
0.5
0.6
0.4
0.6
0.3
1.7
1.5
0.6
0.5
0.4
0.3
0.4
0.3
1.2
0.9
0.4
0.3
0.3
0.3
0.3
0.2
0.9
0.8
0.5
0.4
0.3
0.2
0.9
0.2
Zn
0.2
0.1
0.1
0.1
0.2
0.1
0.2
0.1
0.2
0.1
0.2
0.2
0.1
0.1
0.1
<0 . 1
o!i
<0. 1
0.1
<0 . 1
0.1
0.1
0.1
<0 . 1
0.1
0.1
0.1
0.1
0.1
0.1
0.3
<0. 1
TSS
27
42
10
15
362
29
53
20
17
44
48
34
17
27
29
12
34
-------
TABLE 8. LIME PRECIPITATION/DILUTION OF THIOUREA-HCL
BOILER CLEANING SYSTEM WASTEWATERS
(Values reported in mg/1)
Dilution
0:1
0:1.
0:1 .
. 0:1
1:1
1:1
1:1
1:1
3:1
3:1
3:1
3:1
10:1
10:1
10:1
10:1
pH
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
8.5
9.5
10.5
12.0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
.Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
0.3
0.2
0.3
0.1
0.4
0.2
0.3
0.2
0.2
<0 . 1
1.3
<0 1
0.2
<0 . 1
o!i
<0 . 1
0^2
<0. 1
0.2
<0 . 1
0.1
<0. 1
0.1
<0 1
0.2
<0. 1
0.2
<0.1
0.1
<0. 1
0.1
Cu
0.5
0.5
0.5
0.5
0.6
0.7
0.3
0.3
0.3
0.3
0.5
0.6
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
Ni
0.4
0.3
0.4
0.3
0.4
0.3
0.4
0.3
0.6
0.6
0.5
0.3
0.2
0.2
0.2
0.2
0.7
0.7
0.3
0.3
0.2
0.2
0.1
0.1
0.4
0.4
0.3
0.3
0.2
0.2
0.2
0.1
Zn
0.1
_-*
0.1
0.1
0.1
0.1
0.1
0.1
0.1
<0 . 1
0.1
0.1
0.1
<0 . 1
o!i
<0 . 1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
<0 1
0.1
0.1
0.1
0.1
0.1
0.1
TSS
42
62
14
61
16
40
21
28
34
295
56
16
44
75
49
27
*Sample lost
35
-------
TABLE 9. LIME PRECIPITATION/DILUTION OF AMMONIATED
CITRIC ACID BOILER CLEANING SYSTEM WASTEWATERS
(Values reported in mg/1)
Dilution
0:
0:
0:
1:
1:
1:
1:
3:
3:
3:
3:
10:
10:
10:
10:
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
pH
9.
10.
12.
8.
9.
10.
12.
8.
9.
10.
12.
8.
9.
10.
12.
5
5
0
5
5
5
0
5
5
5
0
5
5
5
0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
2800
2700
270
270
1
0
1200
990
120
38
31
14
4
1
150
64
9
2
1
0
1
0
15
1
1
0
0
0
0
0
.2
.3
.4
.2
.6
.6
.8
.2
.3
.7
.5
.3
.3
.1
.4
.7
.3
.6
.3
Cu
87
95
44
42
5.0
4.8
37
36
17
15
9.0
8.4
0.3
0.2
0.3
0.1
0.3
0.2
0.3
0.3
__*
0.1
0.2
0.1
0.2
0.1
0.2
0.2
0.1
0.1
Ni
65
59
32
28
2
2
269
262
124
102
64
31
3
2
152
152
49
49
4
4
2
0
24
19
2
2
0
0
0
0
.2
.2
.6
.7
.3
.1
.1
.7
.6
.3
.9
.6
.7
.7
.4
.3
Zn
4.2
3.9
1.1
0.7
0.5
0.4
3.9
3.5
0.9
0.3
0.1
<0 . 1
0.1
0.1
0.4
0.4
0.2
0.1
0.1
<0. 1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
<0 . 1
0.1
0.1
TSS
29
258
45
1041
577
35
39
505
35
37
44
78
33
33
27
*Sample lost
36
-------
TABLE 10. SUMMARY OF BEST RUNS FOR LIME PRECIPITATION/
DILUTION OF SIX BOILER CLEANING WASTEWATERS
(Values reported in mg/1)
Supernatant Residuals (Total)
System
Description
Ammoniated
Bromate/HCl
Ammoniated Citric
Acid (Citrosolv)
Ammoniated EDTA
(Vertan)
Thiourea-HCl
System
Hydroxyacetic-
Formic Acid
System
Thiourea-HCl/
Citric System
pH
10.5
12.0
10.5
10.5
10.5
12.0
12.0
8.5
10.5
10.5
10.5
9.5
10.5
9.5
10.5
9.5
10.5
Dilution
Ratio
1:1
1:1
3:1
10:1
10:1
10:1
10:1
0:1
0:1
1:1
3:1
10:1
10:1
1:1
1:1
3:1
3:1
Fe
0.3
0.3
0.2
0.3
0.7
0.6
0.5
0.3
0.4
0.2
0.1
0.8
0.5
0.5
0.3
0.5
0.3
Cu
0.5
0.3
0.5
0.1
0.2
0.1
0.1
0.5
0.6
0.2
0.2
0.4
0.5
0.7
0.6
0.4
0.3
Ni
0.3
0.2
0.3
0.3
0.7
0.4
6.8
0.4
0.4
0.2
0.2
0.3
0.1
0.6
0.4
0.4
0.3
Zn
0.4
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.3
0.2
0.1
0.1
0.1
TSS
37
45
4
15
33
27
22
42
14
21
56
31
23
29
53
44
48
37
-------
,2
pH
Figure 1. Ammoniated Citric Acid System
Iron Residual vs. pH at Four Dilutions
with Fireside Washwater
38
-------
PH
Figure 2. Ammoniated Citric Acid System
Copper Residuals vs. pH at Four Dilutions
with Fireside Washwater
39
-------
PH
Figure 3. Ammoniated Citric Acid System
Nickel Residual vs. pH at Four Dilution
Ratios with Fireside Washwater
40
-------
s
N
PH
Figure 4. Ammoniated Citric Acid System
Zinc Residual vs. pH at Four Dilutions
with Fireside Washwater
41
-------
10,000
8,000
Figure 5. «
Total Suspended^olis.vs.
42
-------
The thiourea-hydrochloric acid (citric acid rinse)
wastewater seemed to follow the general trends for all
metals. Its residuals were low compared to those of other
wastewaters, and did not present a treatment problem.
Metals residuals for the straight thiourea/hydrochloric acid
wastewater were the lowest found, being under 1 mg/1 for all
metals at a 0:1 dilution and a pH of 8.5.
The ammoniated citric acid wastewater also seemed to
complex metals introduced by the diluent, as nickel resi-
duals were observed to increase upon dilution to 1:1, with a
subsequent decrease upon further dilution. Iron was ex-
tremely high at the lower pH and dilution range, but dropped
off quickly with an increase in both parameters, following
the general trends. Copper and zinc also followed the
general trend. Acceptable metal residuals were found only
at a dilution of 10:1 and a pH of 12.0.
Observation of the data in Tables 4 through 9 indicated
that in some cases values for total metals were lower than
the corresponding dissolved metal values. This was particu-
larly apparent in nickel analysis when levels were higher
than 1 mg/1. However, statistical analysis (student's
t-test for related measures) indicated that no significant
difference existed and the data were within the limits of
statistical variability.
The "best runs" for each cleaning system wastewater are
presented for comparison in Table 10. Best runs are based
on pH and dilutions yielding metal residuals substantially
lower than 1 mg/1. For many of the chemical cleaning waste-
waters, a number of different conditions give comparable
results. Where a decision has to be made with respect to
ease or difficulty of treatment, the economic aspect of pH
and dilution becomes important and the lower pH's and dilution
ratios are given priority.
The ammoniated bromate-hydrochloric acid and the two
thiourea-hydrochloric acid systems appear to be easiest to
treat, with all total metals reaching 0.5 mg/1 or less at a
pH of 10.5 and dilution of 3:1. Hydroxyacetic-formic acid
ranks next in ease of treatment, with all total metals less
than or equal to 0.5 mg/1 at a pH of 10.5 and a dilution of
10:1. The ammoniated citric acid and ammoniated EDTA systems
appear as the two systems most difficult to treat. Total
metal residuals for the two systems at a pH of 12.0 and a
10:1 dilution appear comparable, except that total and
dissolved nickel values for the ammoniated EDTA composite
were 6.8 and 5.5 mg/1, respectively. These values are well
above the goal of 1 mg/1, and for this reason, the ammoniat-
ed EDTA system can be considered the most troublesome waste-
water with respect to lime treatment technology.
43
-------
C. Lime Precipitation/Polymers Testing
The effect of using polymers in conjunction with lime
precipitation and dilution to treat the six boiler tubeside
chemical cleaning wastes was investigated as the next phase
in the testing program. Four polymers were to be used at
four different dosages. The selection of polymers and
starting dosages was based on vendor recommendations and
previous experience with use of polymers by the industry.
Four polymers were selected for initial testing, which
include Betz 1115L (liquid, anionic), Nalco 7766 (liquid
anionic), Dow XD-7817.01 (solid, nonionic), and Hereofloc
815 (solid, cationic). The Betz, Nalco, and Hercofloc
polymers were recommended by manufacturers for the treatment
of metal-laden wastewaters. A similar Dow nonionic polymer
was used successfully in the treatment of an ammoniated EDTA
cleaning wastewater sample (33). Early in the testing
program, Magnifloc 834A (solid, anionic) was substituted for
the Hercofloc 815 polymer, which yielded poor results.
Magnifloc 834A was selected as a substitute because it was
used in a previous treatability study of wastewaters from an
ammoniated EDTA cleaning (34).
1. Preliminary Testing
A preliminary run using the initial four polymers was
conducted. The ammoniated EDTA system, which was the most
troublesome system from the lime precipitation experiment,
was used to determine dosage ranges for each polymer and the
better of two mixing cycles. Replicates of the ammoniated
EDTA system wastewater diluted 10:1 with the fireside/air
preheater composite and limed to a pH of 12.0 were employed
in the testing of the initial four polymers. Two polymer
dosages, presumably representing high and low values with
respect to the recommended dosage range, were used in this
run. The dosages are listed below:
(a) Betz 1115L - 0.5 ppm, 2 ppm
(b) Nalcolyte 7766 - 1 ppm, 3 ppm
(c) Dow XD-7817.01 - 0.0025 ppm, 0.05 ppm
(d) Hercofloc 815 - 5 ppm, 10 ppm.
The two mixing cycles chosen differed only in the duration
of slow mixing (30 rpm), one being 10 minutes and the other
20 minutes. Polymers were added to the limed replicates
during rapid mix (RM) at 100 rpm. Approximately fifteen
44
-------
seconds after polymer addition, the slow mix cycle (SM) was
initiated.
After the slow mix period, the samples were settled for
24 hours. Supernatant samples were drawn off after one hour
and four hours settling and analyzed for total suspended
solids. After 24 hours settling, the remaining supernantant
was also analyzed for total suspended solids.
Results are presented in Table 11. It is apparent that
Betz 1115L performed better at the longer mixing cycle and
the higher concentration. The Nalcolyte polymer performed
better at 1 ppm with the shorter mixing cycle. Dow XD7817
performed better at 0.0025 ppm using the longer mixing
cycle. Hereofloc 815, the only cationic polymer used,
performed poorly in all but two cases. It was decided that
for future testing, the Hereofloc polymer should be replaced
with another polymer, preferably not cationic. Magnifloc
834A (solid, anionic) was substituted, since it had previously
been used in a similar lime treatability study. The dosages
selected were based on manufacturer's recommended ranges,
and the longer mixing mode was selected, since it performed
better with three out of the four polymers previously tested.
TABLE 11. PRELIMINARY TESTING OF POLYMERS WITH
AMMONIATED EDTA WASTEWATER COMPOSITE
(All values in mg/1)
Polymer
Betz 1115L
Nalcolyte 7766
Dow XD7817.01
Hercofloc 815
Dosage
0.5
2.0
1.0
3.0
0.0025
0.05
5.0
10.0
10 Minute Slow Mix
Total Suspended Solids
After Settling
20 Minute Slow Mix
Total Suspended Solids
After Settling
1 hr
26
23
45
26
27
115
57
36
4 hr
25
21
12
29
18
72
50
26
24 hr
24
13
10
24
17
28
33
45
1 hr
83
23
29
12
14
26
32
42
4 hr
35
0
16
31
10
27
31
37
24 hr
44
0
16
36
15
20
31
25
The polymer dosage ranges selected for the next phase
of testing were based on levels that showed optimum perform-
ance .
45
-------
2. Determination of Best Treatment Levels Using Dilution-
Lime Precipitation - Polymer Addition Technology
This phase of testing was employed in order to deter-
mine the best treatment levels attainable for each cleaning
system wastewater using dilution, lime precipitation, and
polymer addition. Based on "best run" values, a "most-
difficult-to-treat" wastewater will then be selected.
Five boiler chemical cleaning wastewater samples were
used in this phase of the testing. The thiourea/hydrochloric
acid (with no citric rinse) was excluded from further test-
ing, since metals levels attained in its previous testing
were all less than or equal to 0.2 mg/1.
For each chemical cleaning wastewater sample, the pH
and dilution ratio showing maximum metal removals from the
previous experiment was designated for testing with selected
dosages and mixing cycles. For sets of parameters showing
comparable metal removal efficiencies, economics became the
deciding factor and the lower pH's and dilution ratios were
chosen. The chemical cleaning systems at selected para-
meters are listed below:
System
Ammoniated Bromate/HCl
Hydroxyacetic-Formic Acid
Ammoniated EDTA
Thiourea-HCl/Citric Acid
Thiourea-HCl
Ammoniated Citric Acid
12.0
9.5
12.0
10.5
10.5
12.0
Dilution
1:1
1
1
10
10:
3:1
1:1
10:1
Four polymers were to be employed at four dosages using
the better of the two mixing cycles as determined in the
preliminary testing. The dosages to be used were also
determined from the previous step. As mentioned earlier,
Magnifloc 834A was substituted for the Hereofloc polymer.
Dosages and the mixing cycle for the Magnifloc polymer were
selected based on manufacturer's recommendations, and re-
sults of previous testing with other polymers. A listing of
the dosages and mixing cycles employed for each polymer is
given below:
Flocculant
Betz 1115L
Nalcolyte 7766
Dow XD 7817.01
Magnifloc 834A
Dosages (ppm)
0.5, 1.0, 1.5, 2.0
0.5, 1.0, 1.5, 2.0
0.0025, 0.01, 0.025, 0.05
0.5, 1.0, 1.5, 2.0
Mixing Mode
RM-15 sec., SM-20 min.
RM-15 sec. , SM-10 min.
RM-15 sec. , SM-20 rain.
RM-15 sec., SM-20 rain.
46
-------
Dilution, pH, adjustment, and polymer addition were
conducted as described in previous procedures. After mixing,
the samples were allowed to settle for a total of 24 hours.
Again, two supernatant samples were drawn off, one after 4
hours of settling and the other after 24 hours. Both super-
natant samples were analyzed for TSS total and dissolved
iron, copper, nickel, and zinc.
The results of this experiment are presented in Tables
12 through 16. In most cases, polymers caused a net reduc-
tion in total and sometimes dissolved metals, as data were
compared to previous runs without polymer addition.
The effect of settling time on metal residuals was
variable and seemed to be dependent on the specific waste-
water. Total suspended solids were also generally lower
with the use of the polymers.
The ammoniated bromate/hydrochloric acid wastewater
seemed to follow the above general observations. With
respect to settling time, total iron was observed to in-
crease slightly at the end of 24 hours, while the other
metals were basically unaffected. Total suspended solids
were considerably lower than those obtained without the use
of polymers. All four polymers seemed to give comparable
results.
The thiourea-hydrochloric acid/citric acid wastewater
seemed to show a decrease in metal residuals caused by the
use of polymers. There was no significant difference between
metal residuals at different settling times. Total suspended
solids were generally lower with the use of polymers. All
four polymers gave comparable results.
The hydroxyacetic-formic acid wastewater showed a
decrease in total iron and copper residuals after 24 hours
settling; however, there seemed to be no significant change
in nickel and zinc residuals. Also, total suspended solids
were generally higher than those experienced without the use
of polymers. Total and dissolved iron decreased signifi-
cantly from 4 to 24 hours settling.
Polymers had varying effects on the ammoniated EDTA
wastewater. No significant effects were observed with
respect to differences in iron, copper, zinc, and total
suspended solids. Nickel residuals varied widely, depending
on the polymer tested. Dow XD 7817.01 yielded extremely
high nickel residuals (15 to 20 mg/1) when compared with the
other polymers. The other polymers yielded nickel values in
the range of 3 to 9 mg/1. No significant effect of settling
times was observed.
47
-------
TABLE 12. DILUTION/LIME PRECIPITATION/POLYMER ADDITION TREATMENT
OF AMMONIATED BROMATE/HCL BOILER CLEANING SYSTEM VASTEVATERS
Four Hour Supernatant RealduaU 24 Hour Supernatant Realduala* *
Layer
(1. Tnlekneaa(2) Fe Cu Nl Zn Fe Oi HI Za
Betz 11151. 0.3 PPM 8.4 2.
1.0 6.3 2.
1.5 6.5 1.
2.0 6.3 2.
Nalco 7766 0.5 6.4 2.
1.0 6.4 2.
1.5 6.6 2.
2.0 6.0 1.
Dow XD. . . 0.0025 6.4 2.
0.01 5.9 2.
0.025 6.3 2.
0.05 6.1 2.
0.4 0.3 0.2 0.3 0.
0.4 0.2 < 0.1 0.1 0.
0.8 0.5 0.3 0.3 0.
1.2 0.8 0.3 0.2 0.
0.9 0.2 0.1 0.1 0.
1.0 0.2 0.1 < 0.1 0.
0.4 0.2 <0.1 <0.1 0.
0.4 0.1 < 0.1 0.1 0.
0.8 0.5 2.4 2.6 0.
0.4 0.2 2.1 2.3 0.
0.4 <0.1 0.1 0.3 0.
0.4 <0.1 0.2 0.3 0.
Cy.ni.ld 634A (1.5 5.9 1.5 d.'j C.3 0.3 0.3 C.
1.0 6.5 1.5 1.0 0.6 0.2 0.2 0.
1.5 6.5 1.7 0.4 0.1 0.4 0.4 0.
2.0 5.9 1.5 0.7 0.3 0.3 0.3 0.
0.6
0.3
0.5
0.6
0.4
0.4
0.4
0.3
0.3
0.3
0.2
0.2
0.4
0.6
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.3 0.
0.5 <0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
23 0.3 < 0.1 0.2 0.
24 1.3 1.3 0.
35 0.5 0.1 0.
27 0.4 0.1 0.
29 0.4 < 0.1 0.
14 3.9 3.8 0.
8 0.4 0.1 < 0.
4 0.4 0.1 0.
17 0.3 0.1 1.
7 0.4 0.1 1.
25 0.3 0.1 0.
26 0.3 0.1 0.
35 0.7 0.5 0.
32 0.4 0.2 0.
42 0.4 < 0.1 0.
0.
0.
0.
0.
< 0.
0.
0.
2.
1.
< 0.
0.
0.
o.
0.
34 0.5 0.2 0.2 0.
0.3 0.3
0.3 0.4
0.3 0.2
0.3 0.3
0.3 0.3
0.8 0.8
0.3 0.3
0.3 0.3
0.2 0.2
0.2 0.1
0.2 0.2
0.2 0.2
0.3 0.4
0.3 0.2
0.2 0.1
0.3 0.3
0.1
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
Tib .
39
38
32
43
I
10
q
1
11
15
6
6
:a
15
!3
0
00
(1) Polymer douge reported In ppa.
(2) Layer thlckneao reported In CB
(3) All •otalB and total impended no lids reported la rag/1.
TABLE 13. DILUTION/LIME PRECIPITATION/POLYMER ADDITION TREATMENT
OF THIOUREA/HCL/CITRIC ACID BOILER CLEANING SYSTEM WASTEWATERS
(3) (3)
Thickness*2* Fe Cu HI Zn Fe Cu Ni Zn
Betz 1115L 0.5 9.
1.0 fr.
1.5 7.
2.0 6.
Hal CO 7766 0.5 8.
1.0 9.
2.0 7.
0.01 4.
0.025 5.
0.05 6.
Cy«n*Mld 834A 0.5 4.
1.0 3.
1.5 9.
2.0 9.
3.4 0.
6.0 < 0.
4.8 0.
5.8 0.
3.4 0.
3.4 1.
9.0 0.
a. 3 o.
7.5 0.
6.8 0.
4.B 0.
8.9 0.
3.6 0.2
3.4 0.1
n.
n
n
0.
0.
0.
0.
n
0
0.
0
0
0
0.
0.2 0.2 0.1 0.
0.2 O.I 0.2 0.
0.2 0.1 0.3 0.
0.2 0.1 0.1 0.
0.
0.
0.
0.
0.
0.
0.
0.
< 0.
0.4 0.1 0.
0.4 0.1 0.
0.1 0.1 < 0.
0.2 0.1 0.
0.2 0.1 0.
0.2 0.1 0.
0.1 0.2 0.
0.1 0.3 0.
< 0.1 0.1 < 0.
f 0.1 0.1 0.
0.
0.
0.
0.
0.
0.
0.
n
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
n
0.
0.
0.
0.
n.
0.
0.
23 2.9 0.3 0.2 <0.
22 0.6 0.3 0.2 0.
23 0.6 < 0.1 0.2 0.
27 0.3 < 0.1 0.2 0.
9 0.6 0.3 0.3 0.
10 0.3 < 0.1 0.3 0.
23 0.2 < 0.1 0.2 0.
30 0.4 0.2 0.3 0.
31 0.2 < 0.1 0.2 0.
11 0.1 < 0.1 0.2 0.
2 0.3 < 0.1 0.2 0.
13 1.3 0.2 0.2 0.
20 1-3 0.2 0.3 < 0.
15 0.4 0.2 0.2 < 0.
17 0.6 0.1 0.1 <0.
0.5 0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
< 0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
n
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0
0.
0.
0.
0.
0.
0.
0.
30
25
9
6
19
26
1
70
42
22
25
it
7
4
0
(1) Polymer douge reported ID pp».
(2) Ltyer thlcknei* reported In CB.
(3) All k*tal« cod impended aolldi reported In
-------
TABLE 14. DILUTION/LIME PRECIPITATION/POLYMER ADDITION TREATMENT
OF HYDROXYACETIC/FORMIC ACID BOILER CLEANING SYSTEM WASTEWATERS
V£>
Betz 1115L (
Nalco 7766
Dow XD. . .
Cyanaatd 834.A
(2) Layer thlctu
(3) All octal*
(3)
Thickness*2* Fe Cu Ni Zn
.5 ppo 7.3 1.4 1.1 O.B 0.3 0. 0.7 O.B 0.12
.0 6.9 1.6 0.9 0.3 0.3 0. 0.6 0.5 0.13
.5 6.9 1.5 0.7 0.4 0.3 0. 0.6 0.7 <0.10
.0 5.8 2.2 0.7 0.3 0.3 0. 0.6 0.6 <0.10
.5 10.5 2.5 1.2 0.8 0.3 0. 0.8 0.7 0.10
.0 9.7 3.0 1.0 0.4 0.3 0. 0.6 0.6 cO.10
.0 9.6 3.1 0.9 0.3 0.3 0.3 0.6 0.5 < 0.10
.0025 9.5 3.0 0.7 0.3 0.3 0.3 0.6 0.5 <0.10
.01 10.5 2.5 0.6 0.2 0.3 0.3 0.6 0.5 c 0.10
.025 9.3 3.4 0.7 0.2 0.3 0.3 0.6 0.5 0.10
.05 9.6 3.1 0.9 0.2 0.3 0.3 0.6 0.5 O.?l
.5 9.2 2.8 0.9 0.3 0.3 0.2 0.6 0.6 0.10
.0 9.7 2.8 0.7 0.2 0.3 0.3 0.6 0.5 <0.10
.5 9.8 2.7 0.9 0.1 0.3 0.3 0.6 0.5 0.11
.0 9.2 2.5 0.9 0.2 0.3 0.2 0.7 0.7 0.11
ien« reported In cm.
and suspended solids reported In ag/1.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
Fo
54 0.3 0.
57 0.8 0.
56 0.6 0.
61 0.6 0.
49 0.8 0.
50 0.2 0.
42 0.2 <0.
53 0.2 <0.
45 0.3 <0.
10J 0.3 0.
43 0.3 0.
65 0.5 0.
60 0.3 <0.
55 0.5 <0.
51 2.4 0.
fll.ni Residual (3>
Cu Nl
0.2 0.2 0.5 0.5 < 0.
0.2 0. 1 0.5 0.4 < 0.
0.2 0.2 0.6 0.5 0.
O.Z 0.1 0.5 0.4 0.
0.2 0.2 0.7 0.5 < 0.
0.2 0.2 0.5 0.4 < 0.
0.2 0.2 0.5 0.4 < 0.
0.2 0. 2 0.5 0.4 < 0.
0.3 0.2 0.5 0.4 0.
0.2 0.2 0.5 0.4 < 0.
0.2 0.2 0.5 0.4 < 0.
0.2 0.2 0.6 0.4 0.
0.2 0.2 0.5 0.4 < 0.
0.2 0.2 0.5 0.4 0.
0.2 0.2 0.9 0.4 < 0.
Zn
0
0
2
0
0
0
0
3
0
0
5
0
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
i. TSS
40
38
43
26
59
39
62
58
52
59
41
74
74
68
76
TABLE 15. DILUTION/LIME PRECIPITATION/POLYMER ADDITION TREATMENT
OF AMMONIATED EDTA BOILER CLEANING SYSTEM WASTEWATERS
Betz 1115L
Nalco 7766
Dow XD. . .
Cyanuld 8 34 A
UY°' 171
Thlelu,M6
Nl
t 4,6 4
4.8 4
4.8 4
5.0 5
5,1 5
9.5 9
20. fl 19
18.5 17
6.9 7
7.5 7
5 <0.
9 < 0.
fl < 0.
I <0.
0 < 0.
1 <0.
.9 <0.
.5 <0.
2 <0.
4 <0.
Zn
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
3
3
2
2
2
3
4
1
3
2
3
Fe
0.2 < 0.
< 0.1 < 0.
0.1 < 0.
2.8 0.
0.3 < 0.
0.2 < 0.
0.2 < 0.
0.2 < 0.
0.4 < 0.
0.2 < 0.
0.2 < 0.
0.2 < 0.
< 0.
< 0.
< 0.
< 0.
< 0.
0.
< 0.
< 0.
< 0.
* 0.
< 0.
< 0.
Cu
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
Nl
5.2 5.3
5.4 5.4
4.7 5.3
5.3 5.7
5.4 5.5
B.8 8,8
17.7 19.9
17.9 19.2
16.9 U.I
7.2 7.1
7.7 7.4
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
Zn
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
60
23
38
22
24
35
60
35
34
38
26
tl
(1) ?Dly«er doM|« reported In ppo.
'21 Uycr thlckmss reported In ca.
O> All nciAli and totil »u*pead«d ftolldi reported
-------
TABLE 16. DILUTION/LIME PRECIPITATION/POLYMER ADDITION TREATMENT
OF AMMONIATED CITRIC ACID BOILER CLEANING SYSTEM WASTEWATERS
Layer
0.
< 0.
p"°"
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
< 0.
0.
0.
< 0.
nc R«»ldi
Cu
< 0.
< 0.
< 0.
'. 0.
< 0.
< 0.
0.
0.
< 0.
< 0.
< 0.
< 0.
< 0.
< 0.
< 0.
< 0.
1 (3)
>Al»
Ni
0.4 0.3 0.
0.3 0.2 <0.
0.3 0.3 <0.
0.3 0.3 <0.
0.3 0.2 <0.
0.3 0.3 <0.
0.4 0.3 <0.
0.4 0.3 <0.
0.3 0.3 0.
0.3 0.3 <0.
0.3 0.2 0.
1.1 0.3 0.
0.3 0.3 0.
0.3 0.3 0.
0.4 0.3 <0.
1.6 0.3 <0.
Zn
6
0
0
0
o
0
0
0
7
0
3
4
0
3
0
0
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
26 0.
22 0.
15 0.
31 0.
22 1.
29 0.
33 2.
38 3.
41 0.
23 0.
33 4.
14 0.
34 0.
29 0.
19 0.
3 0.
Fe Cu
<0.1 0.1 <0.
0.1 <0.1 <0.
<0.1 <0.l <0.
<0.1 <0.l <0.
<0.1 <0.l <0.
«0.1 <0.1 <0.
1.7 0.2 0.
2.6 0.2 0.
<0.1 <0.l <0.
cO.l <0.1 <0.
cO.I 0.1 <0.
<0.1 0.3 <0.
<0.1 0.1 <0.
<0.1 0.1 <0.
i 0.3 <0.l <0.
cO.l cO.l cO.
Hi
0.3 0.3 <0.
0.3 0.3 <0.
0.4 0.3 0.
0.3 0.2 <0.
0.5 0.2 <0.
0.3 0.2 0.
0.6 0.4 <0.
0.6 0.5 <0.
0.4 0.4 <0.
0.3 0.2 <0.
0.8 0.2 <0.
0.3 0.2 <0.
0.3 0.2 <0.
0.3 0.2 <0.
0.3 0.3 <0.
0.3 0.3 0.
Zn
0
0
2
0
,
0
0
0
o
0
0
0
0
0
0
5
0.
0.
0.
0,
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
;7
JB
25
U
25
26
60
74
26
11
71
7
135
25
30
13
(1 > Polymer doug« i
(2) Layer thickness
(3) HetBla And tot«:
(i) Supernatant »an[
sported In ppo.
reported In cm.
-------
The ammoniated citric acid wastewater data showed no
significant differences in metal residuals with respect to
the use of polymers. Some very low supernatant suspended
solids values were obtained, suggesting enhanced clarifica-
tion by the use of polymers for this particular system.
Little if any effect could be attributed to differences in
settling time.
It is important that total iron at the end of 24 hours'
settling seems to be somewhat variable. This is believed to
be caused by entrainment of solids during the second decant-
ing, since the sludge interface is much closer to the decanting
apparatus during this operation.
A summary of "best runs" is presented in Table 17.
Best runs were selected by observing which runs gave best
overall performance based on metal and suspended solid
residuals and sludge volume. Where two dosages of the same
polymer gave comparable results, the lesser of the two
dosages was selected as the best run, for economic reasons.
The data show that for most systems, the 1 mg/1 limi-
tation is attainable on a laboratory scale. Also, suspended
solids residuals were below 30 mg/1 for most systems. Table
VII-14 clearly indicates two exceptions:
(a) Values for supernatant total suspended solids for
hydroxyacetic-formic acid appear high. Out of all
runs on Table VII-12, only two showed suspended
solids below 30 mg/1 (one is shown as a best run).
(b) Supernatant nickel residuals are extremely high
for the ammoniated EDTA wastewater, being at least
3.1 mg/1 for total nickel. Since it is understood
that EPA is planning to limit nickel and zinc
emissions as well as iron and copper, this becomes
an important consideration.
With respect to the hydroxyacetic-formic acid system,
it is important to note that suspended solids levels ob-
tained in previous testing (no polymers) at the higher pH
levels were as low as 2 mg/1 in some cases and were generally
lower than those experienced with the use of polymers.
Supernatant from such treatment may have to be filtered
prior to discharge if polymers are used.
A problem does seem apparent when observing treatment
data for ammoniated EDTA. This problem involves the high
nickel residuals in the supernatant. Evidence suggests that
nickel forms a strong bond with the tetra-ammonium EDTA salt
used in the cleaning formulation. It was observed that the
dissolved nickel level in the fireside/air preheater waste-
51
-------
TABLE 17. SUMMARY OF BEST RUNS FOR DILUTION/LIME PRECIPITATION/POLYMER
ADDITION TESTING OF FIVE BOILER CLEANING WASTEVATERS
(All metals and suspended solids reported in mg/1)
Supernatant Residuals
System Description
Ammoniated Bromate/
HC1 (Dilution to 1:1;
pH-* 12)
Thiourea/HCl
(Dilution to 3:1;
pH-* 10.5)
Hydroxyacte tic/ Formic
Acid (Dilution to 10:1;
pH-9.5)
Ammoniated EDTA
(Dilution to 10:1;
PH-12)
Ammoniated Citric Acid
(Dilution to 10:1;
pH -*12)
Polymer Dosage (ppm)
Dow XD. . .
Cyanamid
834A
Nalco 7766
Dow XD.. .
Naclo 7766
Betz 1115L
Betz 1115L
Nalco 7766
Betz 1115L
Dow XD. .
0.
1.
2.
0.
1.
2.
2.
2.
2.
0.
05
5
0
025
0
0
0
0
0
01
Settling Time (hr)
4
it
24
24
24
24
24
24
24
24
Total Fe
0
0
0
0
0
0
0
0
0
0
.2
.2
.2
.3
.2
.6
.2
.2
.2
.1
Total Cu
0
0
0
0
0
0
< 0
0
< 0
< 0
.2
.1
.2
.1
.2
.2
.1
.1
.1
.1
Total Ni
0
0
0
0
0
0
3
7
0
0
.1
.1
.1
.2
.5
.5
.1
.4
.3
.3
Total
< 0.
< 0.
< 0.
< 0.
< 0.
0.
< 0.
< 0.
< 0.
< 0.
Zn
1
1
1
1
1
1
1
1
1
1
TSS
2
15
1
6
39
26
10
21
14
11
N3
-------
water was 195 mg/1, which may further contribute to an
unfavorable equilibrium condition for attaining levels below
1 mg/1 by lime precipitation.
As discussed earlier, in some cases total nickel values
were lower than their dissolved counterparts; however, these
values were within statistical limits. For data interpre-
tation purposes, the higher of the two values should be
considered indicative of the total concentration.
D. Optimization Testing of the Ammoniated EDTA
System Wastewater
After review of the data generated from the previous
investigations, the ammoniated EDTA cleaning wastewater was
selected for representing the "most-difficult-to-treat" of
the five basic kinds of cleaning system wastewaters. The
main criterion for its selection was the fact that superna-
tant nickel residuals could not be reduced below 3 to 4 mg/1
and that nickel is presently considered as much as 5 times
as toxic as copper (35). The major direction in optimiza-
tion testing for the ammoniated EDTA wastewater was (a) to
introduce a pretreatment step in an effort to reduce nickel
levels in the supernatant, and (b) to minimize the diluent
and lime requirements for effective treatment of the waste.
Three preliminary tests were required to determine what
pretreatment practices, if any, would facilitate the removal
of nickel from the ammoniated EDTA wastewater. These tests
and the subsequent investigations that followed are described
below.
1. Investigation of Pretreatment Effectiveness
The effects of aeration, oxidation via hydrogen per-
oxide, and pretreatment of diluent were investigated to
determine if nickel residuals could be reduced below 2 mg/1,
As mentioned above, three sets of preliminary experiments
were conducted in order to gather the required data.
The first experiment consisted of five different treat-
ments. Three 100-ml aliquots of the ammoniated EDTA waste-
water (not diluted) were limed to a pH of 11.0 and aerated
to reduce ammonia concentration. The three aliquots were
then dosed with 0.5 percent, 1.0 percent, and 2.0 percent
hydrogen peroxide, respectively and allowed to react until
bubbling (if any) had subsided. A fourth aliquot of the
ammoniated EDTA wastewater was aerated but did not undergo
pH adjustment, and was dosed with 2 percent hydrogen per-
oxide. The fifth aliquot did not undergo any of the above
53
-------
pretreatments for it was the control. All five beakers were
then diluted with a 10:1 ratio of fireside/air preheater
wash wastewater and limed to a pH of 12.0. The samples were
dosed with 2 ppm Betz 1115L polymer, rapid mixed for 15
seconds, slow mixed for 20 minutes, and allowed to settle
for 24 hours. The supernatant was analyzed for total and
dissolved nickel, iron, and copper.
After this first experiment, further investigation into
the chemistry of hydrogen peroxide oxidation indicated that
the optimum pH for oxidation was in the range of 4.0 to 5.5
(36). A second experiment was run in order to determine the
effect of hydrogen peroxide addition within this pH range.
Again five different treatments were investigated. First,
five 100-ml aliquots of the ammoniated EDTA wastewater (not
diluted) were aerated as is (pH of 9.4). Three of these
aliquots were adjusted to a pH of 4.5 with 1+1 t^SO/ and
dosed with 0.1 percent, 0.5 percent, and 1 percent hydrogen
peroxide, respectively, and allowed to react overnight. The
fourth aliquot was first diluted to a 10:1 ratio with fire-
side/air preheater wash wastewater, then adjusted to a pH of
4.5 and dosed with 0.5 percent hydrogen peroxide. The fifth
aliquot did not undergo any treatment (excepting aeration)
for this was the control. After their respective treat-
ments, the aliquots were diluted (if not already done so) to
a 10:1 ratio with fireside/air preheater wash wastewater and
limed to a pH of 12.0. All treatments were dosed with 2 ppm
Betz 1115L polymer, rapid mixed for 15 seconds, slow mixed
for 20 minutes, and allowed to settle for four hours. The
supernatant after settling was analyzed for total and dis-
solved nickel, iron, and copper.
The third experiment was conducted to investigate the
combined effects of peroxide oxidation, and the use of
pretreated fireside/air preheater wash wastewater, ferrous
sulfate, and lime/caustic soda pH adjustment. Six different
treatments were incorporated in the experiment. All runs
except #6 concluded with liming to a pH of 12.0 with addi-
tion of 2 ppm Betz 1115L polymer, 15-second rapid mix,
20-minute slow mix and four hours settling. Total and
dissolved nickel and iron in the supernatant were analyzed.
The treatments differentiating each of the six runs are
listed below:
Run #3a - A 10:1 mixture of ammoniated EDTA wastewater
and pretreated fireside/air preheater wash
wastewaters was adjusted to pH 5.5 with
l^SO/, dosed with 200 ppm ferrous sulfate and
0.5 percent H909 and allowed to react over-
night. z z
54
-------
Run #3b - An aliquot of ammoniated EDTA wastewater was
adjusted to pH 5.5 with H-SO/, dosed with 200
ppm ferrous sulfate and 1 percent H^®?,
allowed to react overnight, and diluted to a
10:1 ratio with pretreated fireside/air
preheater wash wastewater.
Run #3c - 500 ppm of ferrous sulfate was added to the
10:1 mixture of ammoniated EDTA and the
untreated fireside/air preheater wash waste-
water at pH of 12.0.
Run #3d - Pretreated fireside/air preheater wash waste-
water was used for the 10:1 mixture with the
ammoniated EDTA waste.
Run #3e - Pretreated fireside/air preheater wash waste-
water was used for the 10:1 mixture with the
ammoniated EDTA waste, and 500 ppm of ferrous
sulfate was added after the mixture had been
adjusted (with lime) to pH 12.0.
Run #3f - A 10:1 mixture of ammoniated EDTA wastewater
and untreated fireside/air preheater wash
wastewater was adjusted to a pH of 9.5 with
lime, and further adjusted to a pH of 12.0
with caustic soda.
The pretreated fireside/air preheater wash wastewater
was prepared by addition of lime to a pH of 10.5, settling
overnight, and filtering through a Whatman #31 filter paper.
The pretreated fireside/air preheater had nickel and iron
concentrations of 0.1 mg/1 and 0.2 mg/1, respectively. The
use of ferrous sulfate for two different functions was
investigated. Ferrous sulfate was added to samples prior to
peroxide addition to enhance formation of free radical
hydroxides (Fenton's reagent) and in turn oxidation of
organics (36). The addition of ferrous sulfate during
coagulation was also conducted for the purpose of effecting
a reduction of any higher oxidation states of nickel back to
the bivalent form (this was done in an attempt to reduce
soluble nickel). The effect of using a combination of lime
and caustic soda was also studied for the purpose of evaluating
what is believed to be a more economical alternative (at
higher pH's) than treatment with lime alone (37).
The results for the three runs are presented in Table
18 so that differences in treatments can be compared against
supernatant residual data.
Much information can be derived from Table 18. It
appears that aeration and oxidation do not enhance the re-
55
-------
TABLE 18. SUMMARY OF PRETREATMENT EFFECTIVENESS
FOR AMMONIATED EDTA SYSTEM WASTEWATER
Ul
Designation
la
Ib
Ic
Id
le
2a
2b
2c
2d
2e
Treatment Conditions - Runs 11 and 12
j Aeration , H202 Oxidation Settling
Aeration pH2 Dilution Dosage pH Time
Yes 11.0 No 0.5X 11.0 24 hours
Yes 11.0 No 1. 01 11.0 24 hours
Yes 11.0 No 2.031 11.0 24 hours
Yes 9.4 No 2. OX 9.4 24 hours
No - No - - 24 hours
Yes 9.4 No 0. IX 4.0-4.5 4 hours
Yes 9.4 No 0.5X 4.0-4.5 4 hours
Yes 9.4 No l.OX 4.0-4.5 4 hours
Yes 9.4 No - - 4 hours
Yes 9.4 Yes 0.5X 4.0-4.5 4 hours
Supernatant Residuals (mg/lj
Fe
Total Dlss.
0.4 <0.1
0.3 <0.1
0.3 <0.1
0.6 <0.1
0.5 <0.1
2.1 <0.1
0.3 <0.1
0.8 <0.1
1.2 <0.1
0.4 <0.1
Cu
Total Dlss.
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
0.1 0.1
0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
Nl
Total Diss.
17 17
16 16
19 20
26 25
12 12
44 44
80 76
68 66
16 16
28 25
Observations
No reaction
No reaction
Slight bubbling
Vigorous bubbling
-
No visible reaction
Delayed reaction,
slight color change
Delayed vigorous reac-
tion; pronounced color
change
-
Immediate vigorous
reaction
Designation
3a
3b
3c
3d
3e
3f
Treatment Conditions - Run 03
., Pretreated H202 Oxidation Other
Aeration Dilution FAPWVT Dosage pH3 Chemicals
No Yes Yes 0.5Z 5.5 200 ppm
ferrous sulfate
No No Yes IX 5.5
No - No - - 500 ppm
ferrous sulfate
No - Yes - -
No - Yes - - 500 ppm
ferrous sulfate
No - No - - Limed to pH-8.5;
adjusted to
pH-12.0 with
NaOH
Settling
Time
24 hours
24 hours
24 hours
24 hours
24 hours
24 hours
Supernataat Residuals (mg/1)
Fe
Total Diss.
0.3 0.6
0.5 0.4
0.6 0.2
0.4 0.1
0.4 0.1
1.4 0.1
Ni
Total Diss.
4.2 4.4
5.0 4.9
13.7 13.2
5.0 4.8
4.9 4.6
17.0 17.0
Observations
Delayed reaction,
color change
Delayed reaction,
color change
-
White sludge
Turned green upon
addition of ferrous
sulfate
Supernatant cloudy
Samples are aerated for 15 minutes.
pH is adjusted with lime or H,SO,.
Sample is diluted to 10:1 mixture before oxidation.
4 t
Fireside/air preheated wash vastewater treatment at pH-10.5 to removal metals.
-------
moval of nickel. A comparison of runs le and 2d can illus-
trate the effects of aeration. The only essential differ-
ences between the two runs are the settling times at which
the supernatants were decanted and the addition of an aera-
tion step to 2d. However, data from Table 15 suggest that
the difference between settling times of 4 and 24 hours is,
at most, about 4 mg/1 nickel. Together, these data suggest
that aeration (15 minutes) has no significant effect on
removal of nickel. With respect to iron, it is apparent
that any differences in total concentration are within the
range of the statistical variation, as shown later in Table
21. It is interesting to note that total iron is higher
than 1 mg/1 for one of the runs (2d) at the end of 4 hours'
settling. Whether aeration would serve to lower lime and
diluent requirements has not been determined, and one can
only conclude that aeration had no effect at that specific
pH and dilution ratio.
The effects of hydrogen peroxide oxidation seem to be
statistically significant. It is believed that very little
oxidation took place during Run #1. Although some bubbling
was observed, this was probably caused mainly by the de-
composition of hydrogen peroxide to water and oxygen. How-
ever, it is interesting to note that nickel residuals were
observed to be slightly higher in the Run #1 samples where
the bubbling was noticed (le and Id). It was later learned
that the optimum pH range for hydrogen peroxide oxidation
was between 4.0 and 5.5 (36) and the second set of runs was
oxidized in a pH range of 4.0 to 4.5. Noticeable reactions
did take place in Runs 2b, 2c, and 2e; that is, although
bubbling with a noticeable color change, the reactions were
not immediate in all cases. Another difference in the
second run is that the samples were allowed to stand over-
night. Upon analysis of the supernatant after lime precipi-
tation and 4 hours1 settling, nickel residuals in oxidized
samples were as much as five times higher than the unoxidiz-
ed control (2d). Nickel was almost three times higher in
the run where no visible reaction was observed (2a). Nickel
was slightly higher in the run which was oxidized at the
10:1 dilution with fireside/air preheater wash. There
seemed to be no significant reduction or increase in iron or
copper residuals caused by peroxide oxidation.
It was hypothesized that the high concentration of
nickel in the fireside/air preheater wash wastewater prob-
ably is contributing to this problem. Also, there is some
evidence £b.at nicke.1 can be oxidized to a higher oxidation
state (Ni or Ni ), which has been found to form soluble
complexes with hydroxide (38). However, the exact nature of
this phenomenon is not known, and attempts to define it
would be beyond the scope of this research.
57
-------
In a further effort to reduce supernatant nickel resi-
duals, two additional treatments were introduced. One
involved the use as a diluent of a pretreated fireside/air
preheater wash wastewater, which had nickel levels of 0.1
mg/1. Also, ferrous sulfate was introduced during liming to
possibly reduce any high-valence nickel. These treatments
were the basis for Run #3. Also investigated were the use
of ferrous sulfate as a coagulant and the use of sodium
hydroxide and lime in combination for pH adjustment.
The results from Run #3 showed a decrease in super-
natant nickel residuals when pretreated diluent was used.
This is evident when data from 3a and 3b are compared with
le. However, comparison of 3a and 3b with 3d suggests that
hydrogen peroxide oxidation does little if any good as far
as nickel is concerned. No significant difference in super-
natant iron residuals is apparent when pretreated diluent is
used. All in all, hydrogen peroxide oxidation is not recom-
mended for treatment of ammoniated EDTA wastewaters contain-
ing significant amounts of nickel. Its use should not be
discounted with other boiler chemical cleaning system waste-
waters or where nickel is virtually absent. However, further
testing is required to determine its usefulness in the above
situation. Ferrous sulfate was used for two purposes in Run
#3. The first purpose was to introduce ferrous ion as a
catalyst to the formation of free radical hydroxide groups
(the essence of the peroxide oxidation reaction). No compari-
son was made with respect to its effect. The second purpose
for introducing ferrous sulfate was to possibly reduce any
higher oxidation states of nickel back to the bivalent form,
so that they could be precipitated. Comparison of Runs le
and 3e suggests that no significant difference in nickel or
iron concentration was caused by addition of ferrous sulfate.
(It is not unusual to have differences of more than 1 mg/1
in replicates analyzed on different days, as will be discus-
sed later in this report.)
An alternative pH adjustment procedure was also in-
vestigated, involving liming to a pH of 8.5 with adjustment
to a pH of 12.0 with caustic soda. Results from this treat-
ment (3f) indicate that supernatant nickel residuals are
significantly higher than in the run using straight lime
(le). Also, total iron values after 24 hours' settling were
high (1.4 mg/1), suggesting that the settling characteris-
tics of the floe created by caustic soda are not as good as
those of the floe created by lime alone. Both of these
observations have been confirmed in the literature. Lime
increases dissolved metal removal in the ammoniated EDTA
wastewater, because the calcium cation has a high affinity
for the EDTA molecule, and readily exchanges with other
metals (39). The sodium cation does not possess this char-
acteristic to any great extent. Also, it has been found
58
-------
that sodium hydroxide floes do not settle as well as lime
floes, possibly because the impurities in the lime enhance
settleability (37).
The last observation to be made from this set of data
is that the control (le) for this experiment was signifi-
cantly higher in supernatant nickel residuals than identical
treatments done in previous testing (see Tables 6 and 15).
This corresponded to the fact that a new container of sample
was started for the pretreatment investigation, and so
provisions for the testing of homogeneity from sample to
sample had to be incorporated in the future testing.
In summary, the only treatment that was found to be
effective in reducing supernatant nickel residuals was the
pretreatment of fireside/air preheater wash wastewater prior
to mixing with the ammoniated EDTA wastewater. It was
recognized that such a treatment scheme was probably econo-
mically infeasible because of the need for two lime treat-
ments, and the selection of a diluent which was low in
nickel would probably be the most practical approach.
However, it should be noted that even this would probably
not reduce nickel levels to below 1 mg/1, unless the am-
moniated EDTA wastewater being treated was originally at or
only slightly above this level. Use of pretreated fireside/
air preheater wash wastewater has been omitted from further
testing, based on the above considerations. None of the
other pretreatments will be investigated further.
2. Optimization of Lime and Diluent Requirements
An effort was made to reduce the requirements for lime
and diluent, since the lime dosage needed to raise the pH to
12.0 averaged about 60 to 75 grams per liter of the 10:1
wastewater mixture, and any reduction in diluent volume
would be a direct reduction in lime requirement. Also, it
was recognized that a pH of 12.0 might be over and above the
pH required, and that a slightly lower pH would reduce lime
requirements and may even result in lower nickel residuals
in the supernatants. No pretreatment steps were involved in
the procedure, for it was decided that pretreatment would
not be further investigated, based on the limited success in
minimizing nickel residuals and the economic infeasibility
of pretreatment.
A 24-run matrix test was conducted in which six dilu-
tions and four pH's were used. The dilutions included 10:1,
8:1, 7:1, 6:1, 5:1, and 4:1 with fireside/air preheater wash
wastewater. The pH's 10.5, 11.0, 11.5, and 12.0 were in-
corporated into the matrix. Treatment consisted of lime
addition, a 15-second rapid mix for polymer addition (2 ppm
59
-------
Betz 1115L), a 20-minute slow mix, and settling for four
hours. Total and dissolved iron and nickel in the super-
natant after four hours' settling were reported, along with
supernatant and sludge layer measurements. From previously
generated data (Table 6), copper data and zinc were expected
to be below 1 mg/1 in all of these runs. Therefore, they
were not analyzed.
The data from the above experiment are presented in
Table 19. The data from this table must be given a close
look to determine accurately the effects of changes in pH
and dilution ratio. The statistical data later presented in
Tables 21, 22, and 23 were used as a basis for analysis.
Since all analyses were done on the same calibration curve,
differences over 1.3 mg/1 and 0.7 mg/1 or more are statisti-
cally significant for total and dissolved nickel, respective-
ly. Differences of over 0.7 mg/1 and 0.1 mg/1 are considered
significant with respect to total and dissolved iron, respec-
tively.
The general trend observed is that supernatant nickel
values increase slowly as the pH and the dilution ratio are
lowered. Nickel concentrations range from 10 mg/1 (dis-
solved) at a 10:1 dilution and a pH of 12.0 to 54 mg/1
(dissolved) at a 4:1 dilution and a pH of 10.5. Iron seems
to stay below 1 mg/1 until the pH is lowered to 10.5. This
trend applies in all cases except at 8:1 dilution at pH
11.0. Iron concentrations then jump to from below 1 mg/1 to
7 to 62 mg/1.
More detailed examination reveals that increases are
not steady, but seem to be a function of the pH and dilution
ratio. As an example, at a 10:1 dilution, nickel values
show a steady increase as a function of a decrease in pH,
while at the 7:1 dilution, differences are not apparent
until a pH of 10.5 is reached. A look at iron at a pH of
10.5 versus various dilutions shows an increase in iron
residual, then a marked decrease at the 6:1 dilution, with a
resuming increase for the rest of the dilution range.
For the particular ammoniated EDTA wastewater sample
being tested, optimization still corresponds to a pH of 12.0
and a dilution of 10:1. However, it is important to note
that the reduction of the lime and diluent requirements may
be possible for other ammoniated EDTA wastewaters. This
sample represents a "worst case" wastewater in that nickel
values before treatment are substantially higher than the
norm. Some of the nickel data at lower dilutions (8:1, 7:1,
6:1), suggest no significant increase in supernatant resid- «
uals in the pH range of 11.0 to 12.0, and so it may be pos-
sible to treat some ammoniated EDTA wastewaters at a pH of
60
-------
TABLE 19. OPTIMIZATION OF LIME AND DILUENT
REQUIREMENTS
(Values reported in mg/1)
Dilution
10:1
10:1
10:1
10:1
8:1
8:1
8:1
8:1
7:1
7:1
7:1
7:1
6:1
6:1
6:1
6:1
5:1
5:1
5:1
5:1
4:1
4:1
4:1
4:1
£H
10.5
11.0
11.5
12.0
10.5
11.0
11.5
12.0
10.5
11.0
11.5
12.0
10.5
11.0
11.5
12.0
10.5
11.0
11.5
12.0
10.5
11.0
11.5
12.0
Fe
Total
14
0.4
0.3
0.3
20
24*
0.4
0.4
34
0.4
0.3
0.3
7
0.3
0.3
0.3
17
0.3
0.3
0.6
62
0.6
0.3
0.3
Ni
Layer
Diss.
14
0.1
0.1
0.1
20
24*
0.1
0.1
32
0.1
0.1
0.1
7
0.1
0.1
0.1
17
0.1
0.1
0.1
62
0.2
0.1
0.2
Total
19
14
12
11
24
20
15
15
23
16
15
15
29
21
21
20
38
37
27
29
53
42
37
32
Sprnt.
Layer
Diss.
18
14
12
10
24
20
15
16
22
16
16
15
29
22
21
20
38
38
29
31
54
43
37
35
Sludge
(cm)
5.6
5.1
4.8
5.3
5.6
5.1
6.1
5.8
5.6
5.3
5.3
5.3
5.1
5.1
5.1
4.8
5.3
5.1
4.8
4.6
5.3
4.8
4.6
4.3
(cm)
4.8
5.3
5.6
5.6
4.6
5.3
5.3
5.3
5.1
5.3
5.3
5.6
5.1
5.3
4.6
6.1
5.1
5.6
6.1
7.1
*This value is suspect.
61
-------
11.0. The same conclusions apply to the dilution ratio as
well, and it may be possible to treat some wastewaters at a
dilution of as little as 4:1. In summary, the minimum lime
and dilutent requirements for successful treatment will be
different for each batch of wastewater, depending greatly on
initial metal concentrations in both the ammoniated EDTA
wastewater and the diluent wastewater. For our particular
wastewater sample, no reduction of the lime or diluent
requirement was possible, and further testing was continued
at a pH of 12.0 and a dilution of 10:1.
E. Statistical Testing
Two experiments were conducted for the purpose of
gathering statistical information to support proper inter-
pretation of data. The first test was conducted in response
to observed significant differences in supernatant nickel
residuals from replicate treatments of the ammoniated EDTA
wastewater, i.e. the control in Table 18 as compared to its
replicate in Table 15. It was found that different sample
containers were used in the two tests. It was suspected
that the aliquots from different containers, originally
believed to be identical in concentration, were actually
somewhat heterogeneous even though the total sample was well
mixed while proportioning to separate sample containers.
Identical lime treatments were conducted on aliquots from
five different containers of ammoniated EDTA wastewater as
described below:
(a) The sample that was being used in lime precipita-
tion and best treatment levels testing
(b) The sample that had just been used in optimization
testing
(c) Two previously unopened containers
(d) A one-gallon aliquot that was refrigerated at 4°C.
Once again, the treatment consisted of diluting the
ammoniated EDTA aliquot to a ratio of 10:1 with fireside/air
preheater wash wastewater, liming to pH 12.0, adding 2 ppm
Betz 1115L polymer, rapid mixing for 15 seconds, and slow
mixing for twenty minutes. After four hours' settling, a
sample of the supernatant was decanted and analyzed for dis-
solved nickel. Results are presented in Table 20.
62
-------
TABLE 20. HOMOGENEITY OF AMMONIATED
EDTA ALIQUOTS
Supernatant
Dissolved Nickel
Source (mg/1)
Sample used in lime precipitation 4.9
testing
Sample used in pretreatment test- 9.7
ing
Unused container #1 9.9
Unused container #2 13.3
Refrigerated sample 12.6
The results indicate that the ammoniated EDTA samples were
probably not entirely homogeneous, even though they were
well mixed before transferring. In subsequent testing, the
sample from unused container #1 was used which was closest
to the average of the five runs (10.1 mg/1). The other
metals may also have variations in their residual concentra-
tions due to sample heterogeneity. However, since values of
iron, copper, and zinc were usually below 1 mg/1, this
effect is not considered consequential at this time.
The second statistical experiment was run to determine
statistical variations in metals analysis, total suspended
solids, lime requirements, and supernatant/sludge layer
thicknesses. Two sets of six treatments each were run and
the total analyses for each set were done separately on con-
secutive days. This approach provided data needed for a
statistical analysis, based on the experimental and analyti-
cal procedure. Day-to-day variation in testing caused by
factors such as humidity, room temperature, and line voltage
fluctuations, were also taken into account by this method-
ology.
Replicates were prepared using the ammoniated EDTA
wastewater sample that yielded nickel values closest to the
averaged nickel residuals from the five samples tested.
63
-------
The replicates were all treated at conditions yielding
the lowest nickel residuals, namely a 10:1 mixture with
fireside/air preheater wash wastewater, a pH of 12.0, the
use of 2 ppm Betz 1115L polymer, rapid mixing for 15 seconds,
and slow mixing for 20 minutes. Two decanters were taken
off the supernatant after settling times of two and four
hours. All analyses conducted in previous testing were
included in this experiment, namely total and dissolved
iron, copper, nickel, and zinc, total suspended solids, and
sludge and supernatant layer thicknesses.
Values obtained for the statistical runs are presented
in Table 21. Sample numbers 1 to 6 and 7 to 12 were analyzed
on consecutive days using different calibration curves.
Student's t-test was used to determine day-to-day
variation in total iron, total nickel, total suspended
solids, layer thickness, and lime requirement. Since copper
and zinc values were not variable, statistical analysis on
these metals was not conducted. The data are presented in
Tables 22 and 23. In Table 22, alpha (a) is called the
level of significance and indicates the probability that the
two samples come from the same population. Traditionally,
an alpha value of less than 0.05 has been the criterion for
"significant difference." An alpha of 0.05 indicates that
there is one chance in 20 that the two sample sets in ques-
tion come from the same population. This level of signif-
icance is also termed the 95 percent level.
The data in Table 22 indicate that day-to-day variation
may be significant in isolated cases. For example, total
iron with four-hour settling time and lime requirement shows
significant day-to-day variation. However, the relation, at
least in the case of iron, appears spurious since the two-hour
iron does not show a similar trend. This apparently spurious
correlation indicates that statistical tests must not be
applied blindly.
Table 23 is a statistical treatment of the data in
Table 21. In this table, s is the unbiased standard deviation
and t refers to the t-statistic when (as defined above) is
0.05. The interval X ± ts is the region in which 95 percent
of the data points should lie, assuming a normal distribution.
There are 19 chances in 20 that the population mean of_the
(normally distributed) sampled population lies within X ±
ts/7"~h, where n = the number of samples.
64
-------
TABLE 21. STATISTICAL TESTING OF REPLICATE TREATMENTS
Sample Settling
No. Time (hr.)
1 2
2 2
3 2
4 2
5 2
6 2
7 2
8 2
9 2
10 2
11* 2
12 2
1 4
2 4
3 4
4 4
5 4
6 4
7 4
8 4
9 4
10 4
11* 4
12 4
Supernatant Residuals '=£/!)
Fe
Total Dlss.
0.5 0.1
1.1 0.2
0.6 0.2
0.4 <0.1
0.4 0.1
0.4 0.1
1.2 0.2
0.5 <0.1
0.6 <0.1
0.6 0.1
0.6
0.6 0.1
0.3 0.1
0.4 0.1
0.4 0.1
0.7 <0.1
0.3 <0.1
0.6 <0.1
1.1 0.1
0.1
0.7 0.1
1.4 0.2
-
0.1
Cu
Total Dlss.
<0.1 <0.1
<0.1 <0.1
<0. 1 <0.1
<0.1 <0.1
<0.1 <0. 1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0. 1 <0.1
<0.1 <0.1
<0.1
<0.1 <0.1
<0.1 <0. 1
<0. 1 <0.1
<0.1 <0.1
<0.1 <0. 1
<0.1 <0.1
<0.1 <0.1
<0.1 <0. 1
<0. 1 <0.1
<0.1 <0.1
<0. 1 <0.1
-
<0. 1 • <0.1
Nl
Total Dlss.
7.7 7.4
7.0 7.4
7.4 8.3
7.9 8.3
7,4 8.3
7.2 7.4
7.8 8.1
7.4 7.4
6.9 7.2
7.4 7.8
6.5
7.0 7.2
7.4 7.7
7.0 7.2
7.2 7.3
7.2 7.4
7.0 7.0
7.5 7.4
7.4 8.0
8.1 7.4
6.8 7.4
6.8 7.8
-
7.4 7.4
Zn
Total Dlss.
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
<0.1 <0.1
-
<0.1 <0.1
TSS
13
45
38
33
26
29
48
8
31
34
-
41
69
24
27
8
16
19
11
0
2
25
-
18
Layer Thickness (cm)
Supernatant Sludge
6.0 7.5
5.8 8.0
5.9 8.6
5.9 8.6
6.0 8.5
6.0 9.0
6.0 7.5
6.3 8.2
5.7 9.3
6.5 8.0
1.0 13.5
6.0 8.7
6.0 7.5
5.8 8.0
5.9 8.6
5.9 8.6
6.0 8.5
6.0 9.0
6.0 7.5
6.3 8.2
5.7 9.3
6.5 8.0
1.0 13.5
6.0 8.7
Lime
Requirement
(g)
61.5
63.8
57.8
57.5
58.3
59.7
52.3
52.3
50.5
57.8
53.4
56.0
61.5
63.8
57.8
57.5
58.3
59.7
52.3
52.3
50.5
57.8
53.4
56.0
Sample No. exhibited only minimal settling.
-------
TABLE 22. RESULTS OF STUDENT'S T-TEST ON DAY-TO-DAY VARIATION*
Layer
Fe Ni TSS Thickness Lime Reg.
t a t a t a t a t a
Student's t-test
2-hour Settling -0.763 oKO.l 1.160 a>0.1 -Or220 a>0.5 -0.9040 a>0.1 4.055 oKO.Ol
Time, Day 1 vs. (df=10) (df=10) (df=9) (df=10) (df=10)
Day 2
4-hour Settling -3.735 cKO.Ol -0.353 a>0.5 1.504 ot>0.1 -0.9040 cKO.l 4.055 a<0.01
Time, Day 1 vs. (df=7) (df=9) (df=10) (df=10) (df=10)
2
*In this table, a reflects the probability that the two samples are identical, and df
refers to the degrees of freedom.
-------
TABLE 23. MEAN, STANDARD DEVIATION, AND CONFIDENCE INTERVAL
FOR DAY-TO-DAY VARIATION
Day 1
2-hour
Settling
(Samples 1-6)
Day 2
2-hour
Settling
(Samples 7-12)
Day 1
4-hour
Settling
(Samples 1-6)
Day 2
4-hour
Settling
(Samples 7-12)
Total Fe
Total Ni
s X ± ts* X ± t sA/n~ X s X ± ts X ± ts//rT
0.6 0.3 0.0-1.4 0.3-0.9 7.4 0.3 6.6-8.2
0.7 0.3 0.0-1.5 0.4-1.0 7.2 0.5 5.9-8.5
0.4 0.2 0.0-0.9 0.2-0.6 7.2 0.2 6.7-7.7
1.1 0.4 0.0-2.8 0.1-2.1 7.3 0.5 5.9-8.7
7.1-7.7
6.7-7.7
7.0-7.4
6.7-7.9
values taken to be zero. Value of t obtained from Fischer & Yates,
Statistical Tables for Biological, Agricultural, and Medical Research, Oliver
& Boyd Ltd. , Edinburgh, 1951 (rather than from previous calculation). The t
calculated and given in Table 21 refers to the variation between two groups
of data while the t used in this table refers to the variation within each
group.
-------
TABLE 23. (Continued)
Total Fe Total Ni
X s X ± ts* X ± t sA/n" X s X ± ts X ± ts//iT
00
Day 1
Day 1
2-hour 31 11 2.7-59 19-43 8.4 0.5 7.1-9.7 7.9-8.9
Settling
(Samples 1-6)
Day 2
2-hour 32 15 0-74 13-51 9.2 2.2 3.5-14.9 6.9-11.5
Settling
(Samples 7-12)
4-hour 27 22 0-84 4-50 8.4 0.5 7.1-9.7 7.9-8.9
Settling
(Samples 1-6)
Day 2
4-hour 11 11 0-42 0-25 9.2 2.2 3.5-14.9 6.9-11.5
Settling
(Samples 7-12)
-------
TABLE 23. (Continued)
Lime Requirement
X s X ± ts X ± ts/jn
Day 1
Samples 1-6 59.8 2.5 53.4-66.2 57.2-62.4
Day 2
Samples 7-12 53.7 2.7 46.8-60.6 50.9-56.5
-------
The X ± ts/y~n~ values for total iron suggest that the
average value for supernatant total iron will rarely exceed
1 mg/1. One value for X ± ts/fn~ for total iron suggested a
higher range (0.1-2.1 mg/1) for the mean, however, this
value was based on a significantly lower degree of freedom
(7 as opposed to 9) than the other values. The X ± ts/y/lT
for nickel suggest that the average value should not exceed
8.0 mg/1, however previous treatment of the ammoniated EDTA
wastewaters from different containers resulted in total
nickel residuals of over 13 mg/1 and this fact should be
considered when determining the statistical validity of the
investigation. The X ± ts/yiT values for total suspended
solids suggests that the average value has a moderate prob-
ability of exceeding the 30 mg/1 effluent limitation guide-
line.
Layer thicknesses were somewhat variable, according to
Table 23; however, this was expected since some of the
sludge layer is lost when the sample is transferred to a
settling jar. There were no observed differences in sludge
layer thickness between two and four hours' settling. It
should be noted that one of the samples (#11) underwent
minimal settling (see Table 21). This fact suggests the
possibility of operational difficulties in full scale lime
treatment and clarification. The reason the sample did not
settle is not known.
The lime requirement to achieve a pH of 12.0 was also
observed to vary significantly. The definite cause for the
variation is not known; however, possible explanations
include day-to-day temperature variation, variation in the
composition of different aliquots of lime, and/or error
introduced by the precision of the weighing method (triple-
beam balance).
F. Sludge Characterization
1. Zone Settling Tests
Sludge settling tests were performed on the five runs
used in the previous section for testing sample homogeneity,
for the purpose of evaluating required settling time with
respect to full-scale feasibility. These settling tests
were conducted during the four-hour settling time used for
the homogeneity experiment. This was accomplished by trans-
ferring the unsettled samples (after slow moving) to 1,000-ml
graduated cylinders and recording the height of the super-
natant/sludge interface with time. Interface heights were
recorded every two minutes for 30 minutes, then every five
minutes for an hour, and then each hour up to 4 hours settling,
70
-------
Interface heights vs. time for the five runs is presented in
Table 24.
Figures 6 through 10 show settling curves for the five
runs. A residue analysis of the sludge before settling was
performed on one sample, with the result being 101,189 mg/1
or 10.1 percent solids. Tangents to the elbows of the
settling curves have been constructed to determine detention
times required to concentrate to a specified solids content.
For example, if 20 percent solids concentration is specified
for the sludge after thickening, the following equation is
used to determine corresponding interface height (40).
where: H-, = interface height
C-, = 20 percent solids
H = initial interface height
C = initial solids concentration.
A horizontal line is extended from H, to intersect tangent
line and a vertical line is extended from this point to read
required settling time. If 10.1 percent solids is the in-
itial concentration before settling, then the detention
times required, as calculated from the five settling curves,
would be as follows:
(a) Run #1 - 1.58 hours
(b) Run #2 - 1.46 hours
(c) Run #3 - 1.46 hours
(d) Run #4 - 1.20 hours
(e) Run #5 -1.60 hours
(f) Average - 1.46 hours.
The above detention times correspond to a conventional
thickener and are not applicable to a pond system.
71
-------
TABLE 24. SLUDGE SETTLING DATA
Interface Height (cm)
Minutes
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
35
40
45
50
55
60
65
70
75
80
85
90
95
155
215
240
Run #1
27.6
27.5
27.0
26.3
25.5
24.9
24.1
23.6
23.0
22.4
21.6
20.9
20.0
19.0
18.1
17.7
17.1
16.6
16.3
16.0
15.6
15.4
15.2
15.0
14.8
14.6
14.5
14.4
14.2
13.8
13.7
13.7
Run #2
28.5
28.3
27.7
27.1
26.5
26.0
25.3
24.7
24.1
23.4
22.5
21.7
20.9
19.8
18.8
18.4
17.6
17.1
16.6
16.3
16.1
15.9
15.8
15.7
15.6
15.6
15.6
15.6
15.6
15.6
15.6
15.6
Run #3
26.6
26.4
26.1
25.5
24.9
24.4
23.6
23.2
22.6
21.9
21.1
20.4
19.5
18.5
17.4
16.9
16.3
15.8
15.5
15.2
14.9
14.6
14.4
14.2
13.9
13.8
13.6
13.4
13.3
12.7
12.7
12.7
Run #4
27.0
26.8
26.3
25.6
24.9
24.2
23.6
22.9
22.3
21.6
20.7
19.9
19.0
17.9
17.1
16.7
16.0
15.5
15.1
14.8
14.5
14.2
14.0
13.9
13.6
13.5
13.4
13.4
13.3
13.0
13.0
13.0
Run #5
26.0
25.7
25.4
24.9
24.1
23.6
22.8
22.2
21.5
20.6
19.7
18.6
17.8
17.4
17.1
16.9
16.3
15.9
15.6
15.3
15.0
14.7
14.5
14.3
14.1
13.9
13.9
13.7
13.6
13.1
13.1
13.1
72
-------
30 r
INITIAL SOLIDS = 10
1 2 3
SETTLING TIME (HOURS)
Figure.6. Settling Curve - Run #1
73
-------
30 r
INITIAL SOLIDS = 10.1%
SETTLING TIME (HOURS)
Figure 7. Settling Curve - Run #2
74
-------
30 r
INITIAL SOLIDS = 10
SETTLING TIME (HOURS)
Figure 8. Settling Curve - Run #3
75
-------
CJ
LU
30
29
28
27
26
25
24
23
22
INITIAL SOLIDS = 10
cc.
21
20
E 19
18
17
16
15
13
12
t
V
1 2 3
SETTLING TIME (HOURS)
Figure 9. Settling Curve - Run #4
76
-------
30 r
INITIAL SOLIDS = 10.U
2 3
SETTLING TIME (HOURS)
Figure 10. Settling Curve - Run #5
77
-------
Conversely, if a definite detention time is required
for supernatant clarification, the corresponding sludge
concentration can then be calculated. A detention time of
two hours would then yield an average sludge concentration
of 22.9 percent solids.
It must be noted that a picket stirrer was not used
during these experiments. The slope of the tangent would
probably be slightly less had a picket stirrer been used,
hence lesser detention times and greater sludge compaction.
However, the data adequately show that a reasonable
amount of time is required for sludge settling, and the
treatment is suitable for full scale-up to a conventional
thickening unit. It is recognized that the thickened sludge
has a high solids content and special transport equipment
would be required.
2. Filterability Testing
For the purposes of assessing the feasibility of de-
watering the lime sludge by filtering, the Buchner Funnel
Test was conducted on the sludges of 5 replicates of the
12-replicate statistical run. The procedure for the test is
as follows:
(a) Prepare the Buchner funnel by placing a wire mesh
or screen under the filter paper to ensure drainage
(see Figure 11).
(b) Moisten the filter paper with water and adjust the
vacuum to obtain a seal.
(c) Condition the sludge if necessary; mix it and
permit it to stand 30 seconds to 1 minute; use 200
ml samples.
(d) Transfer it to the Buchner funnel, allow suffi-
cient time for a cake to form (5 to 10 seconds),
and apply the vacuum.
(e) Record the ml of filtrate after selected time
intervals (usually 5 to 10 seconds).
(f) Continue filtration until the vacuum break
78
-------
NO. 2 BUCHNER
FUNNEL
WHATMAN NO. 2 PAPER (7 CM)
WIRE SCREEN
VACUUM GAUGE
NO. 11 STOPPER
PINCH CLAMP HERE AT
START OF TEST
TO VACUUM
PUMP
j)
loo-
80-
80-
ro-
60-
so-
4O.
50-
20-
10-
CALIBRATED HYDROMETER
CYLINDER
Figure 11. Apparatus for Biichner Funnel Test
79
-------
(g) Determine the initial and final solids in the feed
sludge and cake
(h) Record the data obtained and calculate the specific
resistance in accordance with the following equa-
tion (41):
r _ 2bPA2
where: r = specific resistance of cake
o
P = vacuum (g/cm )
2
A = filtration area (cm )
(j = filtrate viscosity (g/sec-cm)
C = weight of solids per unit volume of
filtrate (%)
b = slope of plot of t/v vs. V
o
V = volume of filtrate (cm or ml)
t = filtration time (seconds)
(i) The weight of solids per unit volume of filtrate
can be calculated from the following equation
(derived from 41):
r C.Cf
C = if
100 (Cf-Ci)
where: C. = Initial solids content (%)
Cf = Final solids content of filter cake
1 (%)
In the test, the volume of filtrate was measured every
five minutes until a vacuum break occurred. Also recorded
were the initial and final solids in the sludge and the
vacuum applied. Filterability data are presented in Table
25.
The following conditions apply to the Buchner Funnel
Test and will be used in subsequent calculations:
(a) Initial total sludge solids = 21.85 percent
(b) Filter diameter = 7 cm
80
-------
TABLE 25. SLUDGE FILTERABILITY TESTING
Filter Cake
(Z Solids)
Run l\
32.7
Run *2
33.1
Run 03
34.6
Run «4
34.9
Run #5
32.9
Time (sec) V(ml) t/V V(ml) t/V V(ml) t/V V(ml) t/V V(ml) t/V
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
Slope (b)
by linear
regression
(sec/cm6)
10 0
15 .33
20 .35
20 .75
26 .77
30 1.00
35 1.00
39 1.02
42 1.07
43 1.16
43 1.3
48 1.25
50 1.3
51 1.37
55 1.36
60 1.33
63 1.35
67 1.34
68 1.40
70 1.43
71 1.48
73 1.51
75 1.53
76 1.58
78 1.60
80 1.63
82 1.65
84 1.67
86 1.69
88 1.70
0.017
10 0
19 .26
27 .37
31 .48
38 .53
41 .61
50 .60
52 .67
55 .73
57 .79
60 .83
62 .89
67 .90
70 .93
73 .96
76 .99
78 1.03
80 1 . 06
82 1.1
85 1.2
88 1.44
90 1.17
91 1.21
92 1.25
95 1.26
97 1.29
0.014
5 0
8 .63
22 .45
26 .58
35 .57
40 .63
46 .65
48 .73
50 .80
52 .86
56 .89
60 .92
62 .97
63 1.03
68 1.03
70 1.07
75 1.07
78 1.09
80 1.13
82 1.16
83 1 . 20
84 1 . 25
85 1.29
88 1.31
0.012
8 0
10 .50
26 .38
33 .45
40 .50
46 .54
50 .60
53 .66
60 .66
62 .73
68 .74
70 .79
75 .80
78 .83
80 .88
84 .89
88 .91
0.009
10 0
20 .25
25 .40
30 .50
38 .53
40 .63
43 .70
50 .70
52 .77
55 .82
58 .86
60 .92
62 .97
65 1.00
68 1.03
70 1.07
72 1.11
74 1.15
76 1.18
78 1.22
80 1.75
83 1.27
85 1.29
88 1.31
0.016
81
-------
(c) Filtration area = d2 = 38.5 cm2
(d) Vacuum = avg. 19.5 in. Hg = 686.4 g/cm
(e) Viscosity of filtrate (water) = 0.01 g/sec-cm.
Calculations for specific cake resistance have been made for
each run using the data shown. Specific resistance is
presented below:
Run No. 1 2 3 4 5 Mean
Specific 1.4 x 105 1.2 x 105 1.1 x 105 8.1 x 104 1.3 x 105 1.2 x 105
Resistance
(sec /g)
These values are much lower than values reported for
the specific resistance of lime sludges from water and
municipal wastewater treatment plants. Typical values for
specific resistance ofQwastewater lime sludges were reported
to range from 1.0 x ICr to 24.0 x 10^ secz/g (42). The
concentrations of solids in the sludge before and after
filtration were typical of lime treatment with respect to
thickening and dewatering (42).
The explanation for the apparent decrease in specific
cake resistance lies with the use of polymer for clarifica-
tion. It is well known that polymers have been used success-
fully to improve the filterability of lime sludges.
In summary, dewatering of the lime sludge seems to
present very little problem and will result in a sludge with
a very high solids content of about 34 percent. The main
will involve sludge transportation since initial sludge
solids content is over 20 percent which is considered too
high for conventional pumping. It is believed that sludge
characteristics will be similar in the treatment of waste-
waters from the other chemical cleaning systems.
3. Sludge and Filtrate Metal Concentrations
Metal concentrations of three settled but unfiltered
lime sludges from the statistical experiment were analyzed
for total residue (percent solids), and total iron, copper,
nickel, and zinc. These values and the calculated con-
centrations of metals in a filtered sludge with an average
of 33.6 percent solids (average solids after filtration) are
given in Table 26. Table 26 also gives metal concentrations
82
-------
TABLE 26. SLUDGE AND FILTRATE METAL CONCENTRATIONS
00
OJ
Fe
Sample Total Diss.
Sludge before 7,540.
Filtration1 7,860
(21.85% Solids) 7,920
Sludge after 11,600
Filtration2 12,100
(33.6% Solids) 12,200
3
Filtrate - <0.1
<0. 1
<0. 1
<0. 1
<0.1
Metal
Cu
Total
79
83
83
121
128
128
-
-
-
Concentration (mg/1)
Ni
Diss. Total Diss.
1,040
1,080
1,070
1,600
1,660
!l,650
0.1 - 8.0
0.2 - 7.3
0.2 - 7.3,
<0.1 - 7.1
0.1 - 6.6
Zn
Total Diss.
38.5
40.7
40.7
59.0
63.0
63.0
<0.1
<0. 1
<0.1
- <0. 1
<0.1
Three sludge samples were analyzed.
Metal values are calculated.
Five filtrates are analyzed.
-------
in the sludge filtrates to determine acceptability for
discharge.
The data show that the resultant dewatered sludge is
very high in toxic metals, particularly nickel. The filtrate
dissolved metals were comparable to supernatant values, and
effluent limitations established for the supernatant should
be applicable to these wastewaters as well.
G. Additional Testing of Ammoniated Citric
Acid and Hydroxyacetic-Formic Acid Wastewaters
Additional testing was conducted on the ammoniated
citric acid and hydroxyacetic-formic acid wastewaters, for
the purposes of optimizing lime and diluent requirements and
evaluating the effects of a low nickel diluent. This final
phase of laboratory work incorporated in the use of (1) the
high nickel fireside/air heater wash wastewater sample from
the oil-fired boiler collected at the start of laboratory
testing; and (2) the newly collected fireside/air heater
wash wastewater from a coal-fired unit, presumably low in
nickel. The two chemical cleaning wastewaters and two
fireside/air preheater wash wastewaters were analyzed for
concentrations of iron, copper, nickel, zinc and total
suspended solids. Results of analysis are presented in
Table 27. Metal concentrations of the three previously
analyzed samples are comparable to original values, shown in
Table 3.
TABLE 27. ANALYSIS OF AMMONIATED CITRIC
ACID, HYDROXYACETIC-FORMIC ACID, AND FIRESIDE/AIR
PREHEATER WASH WASTEWATERS
istewater
;tic-Formic
1 Citric Acid
\ir Preheater
>site (Oil-Fired)
Mr Preheater
jsite (Coal-Fired)
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Fe
7110
7600
3600
3150
4200
1100
2000
1300
Cu
0.2
0.1
91
86
14
12
3.2
2.6
Ni
9.0
8.0
51
47
600
660
7.7
7.5
Zn
2.3
2.2
4.7
4.2
19
21
3.0
2.6
TSS
86
Acid
745
15,000
6600
Laboratory testing consisted of dilutions of the chemical
cleaning wastewaters with one of the fireside/air preheater
wash wastewaters, addition of lime to specified pH, settling
84
-------
for 24 hours, and analysis of supernatant for total and
dissolved iron, copper, nickel, and zinc and total suspended
solids. A summary of the various pH's and dilutions used
for the two chemical cleaning wastes is given below:
Diluent 2M Dilution Ratio
Citrosolv System Waste:
(1) Fireside/Air Preheater 10.5 5,7,10
Wash from Oil-Fired
Boiler (High Ni) 11.0 5,7,10
(2) New Fireside/Air Preheater 10.0 1,3,5,7
Wash from Coal-Fired Boiler 10.5 1,3,5,7
(Low Ni) 11.0 1,3,5,7
HAF System Waste
(3) Existing Fireside/Air Pre- 10.5 3,5,7
heater Wash from Oil-Fired 11.0 3,5,7
Boiler (High Ni)
(4) New Fireside/Air Preheater 10.0 1,3,5,7
Wash from Coal-Fired Boiler 10.5 1,3,5,7
(Low Ni) 11.0 1,3,5,7
The specific dilution ratios and pH's used in testing
with the "oil-based" fireside/air preheater wash wastewater
were developed in order to complete total range of dilu-
tions, which is incomplete between the 3:1 and 10:1 dilu-
tions, as shown in Tables 5 and 9. Also, the two pH's were
chosen in an effort to investigate lower lime dosages, as it
is generally agreed that a lime treatment system operating
at pH 12.0 would be troublesome.
The specific dilution ratios and pH's used in testing
with the "coal-based" fireside/air preheater wash wastewater
were developed from data in Tables 5 and 9, taking into
account that lower pH's and dilution ratios would be needed
because of the anticipated lower diluent nickel concentra-
tions. The expectation proved true, as can be seen from
Table 27. In fact, all metals tested were significantly
lower in the fireside/air preheater wash wastewater from the
coal-fired unit than that of the oil-based.
The results of lime precipitation/dilution studies for
the ammoniated citric acid wastewater are given in Table 28.
Results of Run #1 along with results given in Table 9 suggests
that supernatant metal residuals substantially below 1 mg/1
85
-------
TABLE 28. ADDITIONAL LIME PRECIPITATION/DILUTION TESTING
OF AMMONIATED CITRIC ACID SYSTEM BOILER CLEANING WASTEWATERS
(Values reported in mg/1)
Run SI - FAPWW1
Dilution
5:1
5:1
7:1
7:1
10:1
10:1
Dilution
1:1
1:1
1:1
3:1
.1:1
3:1
5:1
5:1
5:1
7:1
7:1
7:1
pH
10.5
11.0
10.5
11. 0
10.5
11.0
Run
P"
I'l.O
10.5
11 .0
10.0
10.5
1 1 .(I
10.0
10.5
11.0
10.0
10.5
II .0
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
n - FAPWW1
Metals
Total
Di ssol ved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Disso 1 vcd
Total
Dissolved
Total
Dissolved
From Oil-Fired Boiler (High Ni)
Fe
0.5
0.2
0.3
0.1
0.3
0.1
0.2
0.1
0.2
0.2
0.3
0.1
Cu
0.4
0.3
0.1
0.1
0.2
0.2
0.1
0.1
0.1
0.1
0.1
From Coal-Fired Boiler
Fe
5/0
280
290
120
no
180
190
100
80
26
17
57
37
8.6
, 2.3
2.3
1.7
1.4
0.4
1.2
0.5
1.4
0.7
Cu
23
24
23
24
0.5
0.5
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
Ni Zn
2.6 <0.1
2.4 <0.1
l.l <0.1
0.9 <0.1
1.2 <0.1
1.1 <0.1
0.7 <0.1
0.5 <0.1
0.7 <0.1
0.5 '0.1
0.4 <0. 1
0.3 <0.1 '
(Low Ni)
Ni Zn
18 0.5
21 0.4
13 0.2
13 0.2
3.5 0.1
3.5 <0.1
2.6 0.1
2.4 <0.1
0.8 <0.1
0.8 <0. 1
0.5 <0.1
0.5 <0.1
0.8 <0.1
0.8 0.1
0.5 0.1
0.4 0.1
0.4 <0.1
0.4 <0.1
0.4 <0.1
0.4 <0.1
0.4 0.1
0.3 <0.1
0.4 <0.l
0.4 <0. 1
TSS
82
62
97
56
92
70
TSS
120
87
38
64
84
40
100
72
27
32
43
39
FAPWW - Fireside/Air Preheater Wash Wastewater
86
-------
fireside/air preheater wash wastewater from the oil-fired
boiler, and a pH of 11.0
Suspended solids were generally higher in Run #1 than
in those shown in Table 9. This corresponded to the fact
that supernantants during this run were observed to be
cloudier than those of similar runs. Upon further examina-
tion, it was found that higher lime dosages were required to
attain desired pH's during this additional testing compared
with dosages during the original testing approximately nine
months before. It is believed that the higher lime dosages
contributed to a greater amount of unsettleable particles
being present in the supernatant, hence a generally higher
suspended solids values. Loss of reactivity due to carbona-
tion during storage is accountable for the higher lime
dosages observed in the latter phase of testing.
These facts suggest that hydrated lime should not be
stored for long periods of time, since process as well as
cost efficiency could suffer. Proper storage of lime includes
the use of air-tight containers for periods of not more than
1 year.
Results of Run #2 in Table 28 reflect the effect of
using a diluent low in nickel. As can be seen, nickel
values of 0.5 mg/1 were attainable at a dilution of 3:1 and
a pH of 11.0. A pH of 11.0 was also sufficient to attain
supernatant nickel residuals below 0.5 mg/1 at a 10:1 dilu-
tion with the high nickel fireside/air preheater wash waste-
water used as diluent. The above criteria suggest that:
(1) a pH of 11.0 or even lower may be sufficient to attain
the desired results; and (2) less dilution is required with
a low nickel diluent.
Table 28 also shows that iron residuals were higher in
Run #2 than in Run #1, if one compares the data from treat-
ments using 5:1 and 7:1 dilutions. At a pH of 10.5 and a
5:1 dilution, both total and dissolved iron residuals were
more than an order of magnitude higher than the results of
the similar treatments in Run #1. These results are not as
pronounced in the runs involving higher pH's and dilution.
However, it can be seen that values of supernatant residual
iron substantially below 1 mg/1 were not attained when the
coal-based fireside/air preheater was used as diluent. A
comparison of the two fireside/air preheater wash waste-
waters in Table 27 indicates that initial iron concentrations
were actually higher in the fireside/air preheater wash from
the oil-fired unit, which seems to conflict with the results
after precipitation.
No scientifically supported hypothesis was formulated
to explain the higher iron residuals in Run #2, however the
87
-------
results demonstrate that iron residuals may not always
attain the 1 mg/1 limit stipulated by EPA when treating
ammoniated citric acid wastewaters. It would have been
helpful if dilutions of 10:1 with the coal-based diluent had
been run, to see if iron levels then dropped below 1 mg/1.
However, the scope of this study did not allow for addi-
tional analytical efforts which could potentially provide
supplementary data adequate to resolve the above uncertain-
ties. Based on previous experience with the effects of
dilution ratio on metal residuals, it is believed that
dilution beyond 7:1 would have yielded total iron levels
below 1 mg/1. However, further testing with the ammoniated
citric acid wastewater and other fireside/air preheater wash
wastewaters including that used in Run #2 is recommended.
Results of testing with the hydroxyacetic-formic acid,
boiler cleaning wastewater (Table 29) indicated that metal
residuals well below 1 mg/1 could be attained for all metals
at dilutions of 5:1 and a pH of 10.5 for the oil-based
fireside wash. Lime requirements for successful treatment
using the coal-based fireside/air preheater wash wastewater
were less, with a pH of 10.0 yielding metal levels well
below 1 mg/1 at the 5:1 dilution. Total suspended solids as
compared to those presented in Table 5, were higher, probably
for reasons similar to those developed above for the ammoniat-
ed citric acid system. High iron residuals did not occur in
Run #2 of Table A, as was the case with the ammoniated
citric acid wastewater.
88
-------
TABLE 29. ADDITIONAL LIME PRECIPITATION/DILUTION
TESTING OF HYDROXYACETIC-FORMIC ACID SYSTEM
BOILER CLEANING VASTEWATERS
(Values reported in mg/1)
Dilution
5:1
5:1
7:1
7:1
10:1
10:1
Dilution
1:1
1:1
1:1
3:1
3:1
3:1
5:1
5:1
5:1
7:1
7:1
7:1
Run
oH
10.5
11. 0
10.5
11.0
10.5
11.0
oH
10.0
10.5
11.0
10.0
10.5
11.0
10.0
10.5
11.0
10.0
10.5
11. 0
//I - FAPWW1 From
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Run 02 - FAPWW1
Metals
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Total
Dissolved
Oil-Fired Boiler
Fe
0.2
=0.1
0.2
C0.1
0.2
0.1
2.0
0.1
0.1
0.6
0.1
from
Fe
0.5
0.4
1.1
0.7
1.5
1.1
0.7
0.2
0.5
0.2
0.4
0.2
0.2
0.2
0.2
0.1
0.4
0.2
0.2
0.1
0.3
0.1
0.2
0.1
Cu
0.2
0.1
0.3
0.2
0.1
0.1
0.]
0.1
0.2
0.1
Coal-Fired
Cu
0.9
0.8
0.7
0.6
0.8
0.7
0.3
0.2
0.5
0.4
0.4
0.4
,1.1
O.I
0.3
0.2
0.2
0.2
0.1
O.I
0.2
0.1
0.1
0.1
(HiRh Ni)
Ni Zn
0.2 <0.1
0.1 <0.1
0.2 <0.1
0.1 <0.1
0.2 <0.1
0.1 <0.1
0.3 <0.1
O.I <0.1
0.2 <0.1
O.I 0.1
0.2 <0.1
0.1 <0.1
Boiler
Ni Zn
0.3 <0.1
0.2 <0.1
0.3 <0.1
0.2 <0.1
0.3 <0.1
0.3 <0.1
0.2 <0.1
0.2 <0.1
0.2 <0.1
0.2 <0.1
0.3 <0.1
0.2 <0.1
0.1 <0.1
0.1 <0.1
0.1 <0.1
0.1 <0.1
0.2 <0.1
0.1 <0.1
0.1 <0.1
0.1 <0.1
0.1 <0.1
0.1 <0.l
0.2 <0.1
0.2 <0.1
TSS
209
71
308
92
870
90
TSS
70
52
50
46
52
46
54
29
32
29
40
38
'rAPWW - Fireside/Air Preheater Wash Wastewater
89
-------
VIII. APPLICABILITY OF LABORATORY TESTS TO
FULL-SCALE TREATMENT
Assessing the applicability of laboratory treatability
data to a full-scale treatment process involves considera-
tion of many factors, including the following:
• Conditions in the field that are not encountered
in bench-scale testing. This includes avail-
ability of diluents, use of substitute diluents,
storage facilities for both chemical cleaning and
diluent wastewaters, and mixing of wastewaters.
• Process conditions in full-scale treatment, such
as changes in flow and temperature, concentration
gradients, and pH controllability.
• Availability of the specific process plant equip-
ment needed for successful treatment of the waste-
water and sludges.
A. Field Conditions
Conditions in the field will be quite different from
the controlled conditions in the laboratory. One important
difference may be the availability and type of diluent
wastewater, and the provisions needed for storage. Dilution
ratios yielding successful treatment ranged from 3:1 to 10:1
for tubeside cleaning wastewaters and ranged from 1:1 for
the ammoniated bromate/HCl wastewater to 10:1 for successful
treatment of ammoniated EDTA wastewater. Lime treatment for
the ammoniated EDTA wastewater is presently not recommended,
based on the fact that supernatant nickel residuals are such
a problem. Therefore, a representative dilution ratio
covering the general treatment of tubeside wastewaters has
been selected based on the ammoniated citric acid waste-
water, the next most difficult to treat. Data in Table 28
suggest that a dilution ratio of 7:1 will be generally
adequate to attain successful treatment of tubeside cleaning
wastewaters, as long as filtration is used (this requirement
is based on data of Run #2, Table 28, in which total iron
did not drop below 1 mg/1 at the 7:1 dilution).
In a full-scale situation, assuming a typical total
volume of chemical cleaning wastewater of 760 m , the cor-
responding volume of diluent wastewater to give a 7:1 dilu-
tion would be 6,080 m . Such a volume would require about
2,533 m of land for a storage pond (2.4 m pond depth).
90
-------
Most power plants could probably provide for this
additional storage area. However, it is less certain whether
a power plant would generate the required volume of fireside
and/or air preheater wastewater for dilution of a specific
volume of tubeside cleaning wastewater. The tubeside cleaning
wastewater might have to be stored until enough fireside/air
preheater wastewater was generated, or a substitute diluent
such as coal pile runoff could be used as a supplement to
attain the desired dilution. Table 30 shows the ratio of
air preheater wash wastewater volume to tubeside cleaning
volume collected over the interval between tubeside cleanings
for four boilers of power plants surveyed during the prepara-
tion of the development document (30). It is obvious that
amounts of available air preheater wash wastewater vary
widely from plant to plant. More detailed data are available
on the flow rates of fireside and air preheater wash waste-
waters that may prove useful in further defining the percent-
age of power plants having an adequate volume of these
diluents (43,44). However, a substantial amount of data
compilation is required, as existing data is presented as a
function of power plant type and capacity, rather than on
the basis of boiler unit. Recommendations to more clearly
define the relative availability of fireside and air preheater
wash wastewaters include compiling fireside and air preheater
data on a boiler unit basis, or perhaps developing data on
flowrates of tubeside cleanings on a plant or megawatt
basis. It seems imperative that such an analysis be conduct-
ed if recommended treatment is to cover the whole steam
electric power generating point source category.
Coal pile runoff would be a suitable alternative or
supplemental diluent wastewater, based on reported loadings
of 64,000 to 32,000^m per year with average figures of
75,000 to 100,000 nr per year (30). It is evident that an
adequate amount of diluent should be available for all
coal-fired power plants. However, for power plants running
entirely on oil or gas, other sources of substitute diluents
may have to be found if there is an inadequate volume of
fireside and air preheater wash wastewater.
The effect of using substitute diluent has not been
investigated in the laboratory. However, comparison of coal
pile runoff wastewaters to fireside/air preheater wash
wastewater used in laboratory testing shows that metals of
concern are present in much lower quantities in the coal
pile runoff. Chemical characteristics of coal pile runoff
from two plants are shown in Table 31. The data suggest
coal pile runoff would be very suitable for use as diluent
in treatment of chemical cleaning wastes.
91
-------
TABLE 30. RATIO OF AVAILABLE AIR PREHEATER WASTEWATER VOLUME TO
TUBESIDE CLEANING VASTEWATER VOLUME (30)
Cleaning Frequency
(yr )
Batch Volume'
(m3)
Plant Boiler Volume
Codez (m-3)
3409
3410
3412
3414
174
106
215
303
Air
Preheater
12
12
12
6
Boiler
Tubes ide
0.5
1
0.5
1
Air
Preheater
409
852
2272
163
Boiler Ratio of ^
Tubeside Collected Volumes
696
424
860
1212
3.5
24
63
0.8
Four cleaning stages were assumed for calculation of batch volume for boiler tubeside
cleanings.
"Refers to number designation of power plant in the EPA development document cited
above.
Refers to ratio of air preheater wash wastewater volumes to tubeside cleaning
volume collected over the interval between tubeside cleanings.
-------
TABLE 31. CHARACTERISTICS OF COAL PILE DRAINAGE (45)
Concentration
mg/1 (unless otherwise indicated)
Constituents
Acidity (total), as CaC03
Calcium
Chemical Oxygen Demand
Chloride
Conductance, umho/cm
Dissolved Solids (total)
Hardness, as CaCCL
Magnesium
pH, unit
Potassium
Silicon (dissolved)
Sodium
Sulfate
Suspended Solids (total)
Turbidity, JTU
Aluminum
Arsenic
Barium
Beryllium
Cadmium
Chromium
Copper
Iron
Lead
Manganese
Mercury
Nickel
Selenium
Titanium
Zinc
Plant J
1,700
240
9
0
2,400
3,200
600
1.2
2.9
--
91
--
2,600
550
300
190
0.01
--
--
0.001
0.005
0.56
510
0.01
27
0.0002
1.7
0.03
1
3.7
Plant L
270
350
--
--
2,100
1,500
980
0.023
2.9
--
--
4.1
--
810
—
—
0.009
0.1
0.01
0.006
0.005
0.18
830
0.023
110
0.027
0.32
0.003
—
1.0
93
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Proportioning and mixing of the chemical cleaning and
diluent wastewaters, although not a problem in the labora-
tory, may present some challenges in the field. Two basic
methodologies for mixing wastewaters in the field are apparent,
The first methodology involves mixing the wastewaters in the
diluent wastewater holding pond. If this method is chosen,
the volume of diluent wastewater in the pond must be known,
so that provisions can be made to attain the proper ratio
for dilution of the chemical cleaning wastewater. Prelimin-
ary testing should be done on a sample of the composite
chemical cleaning wastewater to determine the minimum dilution
requirement along with other parameters. The chemical
cleaning wastewater should be held in temporary storage if
the volume of diluent water in the holding pond is excessive,
so that the excess can be pumped out and minimum costs are
incurred during treatment. The chemical cleaning waste can
be added directly to the diluent holding pond if the diluent
volume is known to be less than the anticipated requirement.
However, the best approach may be temporary storage of the
chemical cleaning wastewaters until treatment parameters
have been established in the laboratory. Mixing the waste-
waters to insure homogeneity can be accomplished in the
diluent holding pond by recirculation or aeration. Mixing
for a few days prior to treatment should insure adequate
homogeneity.
The second methodology for proportioning and mixing
wastewaters would require separate storage facilities for
chemical cleaning waste and diluent wastewater. Proportion-
ing the wastewaters would be accomplished by controlling
flow rates as the two wastewaters were pumped into an equal-
ization pond. Mixing in the equalization pond could be
accomplished by aeration, recirculation, and/or proper
baffling. This second methodology introduces the additional
advantage of treating the chemical cleaning waste a little
at a time as the diluent wastewater becomes available, thus
reducing storage requirements.
In summary, it is believed that, although field condi-
tions may present challenges in some cases, diluting chemical
cleaning wastewater with fireside and air preheater washings,
coal pile runoff, or another suitable diluent is applicable
to full-scale treatment at most power plants.
B. Process Conditions
Process conditions that may be present in full-scale
treatment must be considered when a laboratory treatability
study is assessed with respect to probable success in the
field. Such conditions include flow, temperature, concen-
tration, and pH variability.
94
-------
Flow variability would have an effect on general re-
moval efficiencies in a full-scale treatment process, because
of resulting variations in pH; detention times for rapid
mixing, slow mixing, and settling; and polymer dosage.
Since the process will involve batch treatment that can be
well regulated by pumping rates, the effects of flow vari-
ability on treatment are expected to be minimal.
Temperature variations are expected to have significant
effects on the efficiency and economics of the full-scale
treatment process. However, temperatures are expected to
vary on a seasonal basis, and should not fluctuate during
the time interval for batch treatment. However, there is a
possibility that a temperature gradient could exist in the
holding pond(s). Since the pond depth is expected to be
relatively shallow (3 m), the temperature gradient in such a
pond is not expected to be greater than 3°C (46). Two
methods are available to minimize any temperature gradient
within the holding pond(s). The first is some form of
mixing, either aeration or recirculation. The second in-
volves treating the waste in mid- to late summer, when the
temperature profile will be almost vertical, with no ef-
fective change in temperature with depth (46).
As mentioned above, the seasonal temperature is most
important, and treatment should be conducted during mid- and
late summer, when water temperature is also highest. Investi-
gations show that an increase in wastewater temperature of
10°C has marked beneficial effects on almost all wastewater
treatment unit operations. Specific references have been
made to increases in temperature resulting in more rapid
floe formations, shorter settling times, and decreased
coagulant (in this case, lime) requirements (47). Table 32
presents a summary of temperature effects on the size require-
ment and efficiencies of various wastewater treatment pro-
cesses .
Variability of concentrations of metals in the un-
treated wastewaters can be introduced by incomplete mixing,
either in the holding ponds or during equalization. The
data in Table 19 give much insight into probable effects,
since changes in dilution ratios can be thought of as changes
in initial metal concentrations. The data suggest that
supernatant residual iron concentrations (both total and
dissolved) will be relatively unaffected by concentration
changes of 100 percent providing the pH is 11.0 or above.
Supernatant nickel residuals (Table 9) at dilution ratios of
7:1 to 10:1 will be relatively unaffected by changes in
concentration provided the pH is maintained above 10.5.
Data from Tables 4 through 9 suggest that, for most systems,
copper and zinc will be unaffected by changes in concentra-
tion, provided a pH above 10.5 is maintained. This assump-
95
-------
TABLE 32. SUMMARY OF UNIT SIZE AND EFFICIENCY
CHANGES DUE TO 10°C TEMPERATURE INCREASE
(20°C to 30°C) (47)
Unit Operation
Change Due to Temperature increase
7o Change in L Change in Unit
Unit Size Efficiency
Grit Chamber
Primary Clarifier
Aeration Basin
Trickling Filter
Stabilization Pond
Aerated Basin
Final Clarifier
Chlorine Contact Tank
Thickener
Anaerobic Digester
Vacuum Filter
Centrifuge
Filtration (Strat.)
Rapid Sand
Backwash Rate
Activated Carbon
Foam Separation
Nitrification
Dentrification (.S.)
Ammonia Stripping
Anaerobic Column
(Nitrogen Removal)
Pure 02 Activitated Sludge
Coagulation
16.!
20
10
68
48
52
20
28
20.'.
38.5
14
20
19
*
*
-8
*
27
92
50
*
*
13
13
12
30
15
8
8.2
9
25
20
60
-16
29
-5
65
47
14
*
28
114
50
*Not calculated
Note: Minus sign indicates an increase in unit size or
a decrease in efficiency. No sign indicates a
decrease in unit size or an increase in efficiency,
96
-------
tion is based on comparison of supernatant residuals at
dilutions of 3:1 and 10:1. The above criteria suggest that
as long as pH is maintained at 11.0 or above, there will be
little change in supernatant metal residuals with respect to
normally encountered variations in untreated wastewater
metal concentrations.
As mentioned above, changes in pH should have little
effect on supernatant metal residuals provided that the pH
is maintained at 11.0 or above. A pH above 11.0 should be
maintained if good clarification is expected, because of the
enhancing effect of magnesium hydroxide precipitation (42).
Therefore, operating at a pH of between 11.0 and 11.5 should
accommodate any fluctuations inherent in pH control with a
straight lime system.
C. Requirements for Process Equipment
and Materials
Treatment of boiler chemical cleaning wastewaters as
practiced in the laboratory is applicable to full-scale
treatment. However some special considerations must be made
with respect to the equipment and materials needed for
specific unit operations. Proportioning and mixing of
wastewaters has been treated in a previous section and will
not be discussed here.
A major consideration with respect to required process
equipment and materials involves high lime requirement for
treatment. Generally, a slurry of lime will be used rather
than the solid form and a softened water is recommended as a
solvent. The slurry could either be mixed from hydrated
lime or purchased as a 20 percent mixture (chemline slurry).
All necessary provisions for a high lime system will be
required, including the use of plugged pipe fittings to
allow cleanout, compatible pumps, and proper pacing and
control systems. Daily maintenance of pH instrumentation
will be essential for adequate control.
The large amount of lime sludge that is expected to be
generated will require a clarifier with a large sludge-
handling capacity. Detention times for suspended solids
removal and zone settling are not abnormally high, and
should present no major problems. It should be remembered
that batch treatment should be conducted during mid- to late
summer, in order to minimize the requirement for lime. The
resulting lime sludge before dewatering was found to contain
an average of over 20 percent solids; therefore, heavy-duty
pumps applicable to lime sludges will be required. Not
enough data were available to assess special requirements
for dewatering equipment.
97
-------
Also, because of the high solids content, a specially
designed flocculator may be necessary, with an aeration
system assisting the rotating paddles to provide adequate
mixing.
Some type of neutralization system will be required, to
adjust effluent pH to between 6.0 and 9.0. Because of the
high pH's required for successful treatment, a recarbonation
system would be more suitable than acid neutralization,
since neutralization by acid would result in a treated
wastewater with very high total solids.
The materials of construction are an important con-
sideration after the lime precipitation and clarification
operations have occurred. It must be recognized that strong
chelating agents will still be present in the supernatant
after treatment. Chelants such as ammoniated EDTA and
citric acid could pick up metals from any source that is
contacted prior to discharge. Sources include piping mater-
ials, neutralization or recarbonation equipment, and filtra-
tion equipment and media (if used). Therefore, equipment
and piping materials following clarification may have to be
fabricated from such non-metal leaching materials as poly-
vinyl chloride. It should be noted that this effect is
possible but not definite. Further experimentation with the
wastewaters under investigation is required before an accur-
ate assessment of this problem can be made.
Filtration may, in some cases, be required for success-
ful suspended solids treatment. In all but one of the
wastewaters (hydroxyacetic-formic acid cleaning system),
suspended solids below 30 mg/1 could be achieved with poly-
mers after four hours' settling. An average of 20 mg/1 was
achieved on the statistical run for the ammoniated EDTA
system after four hours of settling. This is considered
representative of the other wastewaters, excepting the
hydroxyacetic-formic acid system. Results from additional
testing of ammoniated citric acid and hydroxyacetic-formic
acid wastewaters (Tables 28 and 29) indicate that the use of
excessive amount of lime (when caused by reactivity loss
upon storage or low reactivity to begin with) could result
in higher suspended solids concentrations in the supernatant
Hence, in a field condition where large amounts of lime may
be stored for long periods of time, and where clarification
may not be as efficient as in the laboratory, filtration
should probably be included in the treatment scheme. Neu-
tralization of the wastewater is necessary prior to filtra-
tion to insure against leaching of iron under alkaline
conditions. To insure against any possible leaching, a
high-purity media containing as little iron and other metals
as possible should be used. Again, the metal pickup proper-
ties of the supernatants have not been adequately treated
and additional research is needed.
98
-------
IX. REFERENCES
1. Woodridge, J. 1978. Personal communication. Dow
Industrial Services, July 28, 1978.
2. Gatewood, J.R. 1978. Personal communication. Halli-
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3. Roebuch, A.M. 1978. Safe Chemical Cleaning the Organic
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4. Reich, C.F. and D.B. Carroll. 1965. A New Low Chloride
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Cleaning Solutions, presented at the American Power
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5. UWAG Priority Pollutants Task Force. 1978. Comments
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6. Budden, K. 1979. Personal Communication. Sheppard T.
Powell Associates, Baltimore, Maryland. March 1979.
7. Gatewood, J. 1979. Personal Communication. Halli-
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8. Gatewood, J. 1978. Personal Communication. Halli-
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9. Babcock & Wilcox. 1972. Steam/Its Generation and Use,
38th edition. Babcock & Wilcox Company, New York, New
York.
10. Shissias, J.A. 1976. Letter to Mr. Richard A. Baker,
U.S. EPA with enclosed report: "Precipitation of
Metals from Chemical Cleaning Solutions." Public
Service Electric and Gas Company, Newark, New Jersey,
May 14, 1976.
11. Martell, A.E. 1976. Critical Stability Constants,
Volume III: Other Organic Ligands. Plenum Publishing
Corporation, New York.
12. Halliburton Services. 1971. Technical Data Sheet
IC-12022. Cutain I Complexing Agent. Halliburton
Services, Duncan, Oklahoma.
13. Kuppusamy, N. March 1977. Copper Removal from Power
Plant Boiler Cleaning Waste. Industrial Waste. 23(2):
43-45.
99
-------
14. Smith, R.M. and A.E. Martell. 1977. Critical Stability
Constants, Volume IV: Inorganic Ligands, Plenum Publish-
ing Corporation, New York.
15. Halliburton Services. 1973. Technical Data Sheet
IC-12005. The Citrosolv Process. Halliburton Services,
Dunkan, Oklahoma.
16. Wackenhuth, E.G., L.W. Lamb and J.P. Engle. November
1973. The Use and Disposal and Boiler Cleaning Solvent.
Power Engineering.
17. Chemical Marketing Reporter. 1978. Current Prices of
Chemicals and Related Materials, Volume 214, No. 6.
Schnell Publishing Company, New York. August 7, 1978.
p. 42-52.
18. Martell, A.E. 1964. Stability Constants of Metal Ion
Complexes. Special Publication No. 17. The Chemical
Society. London.
19. California Regional Water Quality Control Board, Santa
Ann Region. 1976. Request for Variance from Effluent
Guidelines Limitations for Steam Electric Power Gener-
ating Point Source Category. Transmittal of August 12,
1976.
20. Halliburton Services. 1968. Technical Data Sheet
IC-12009 (revised) Hydroxyacetic/Formic Acid. Halli-
burton Services, Duncan, Oklahoma.
21. Sisson, A.B. and G.V. Lee. 1972. Incinceration Safely
Disposes of Chemical Cleaning Solvents. Presented at
American Power Conference.
22. Dow Industrial Service. 1975. Boiler Tube Deposits
Like This Are Effectively Removed by Alkaline Copper
Removal (ARC). Form No. 174-402-75. Dow Chemical,
Midland, Michigan.
23. Smith, R.M., and A.E. Martell. 1974. Critical Sta-
bility Constants, Volume I: Amino Acids. Plenum Publish-
ing Corporation, New York.
24. Broust, C. 1979. Personal communication. Gallatin
Steam Plant (TVA), Gallatin, Tennessee. March 14,
1979.
25. Kniff, K.J. 1979. Letter to Paul J. Rogoshewski,
Hittman Associates, Inc. Allegheny Power System.
Greensburg, Pennsylvania. February 23, 1979.
100
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26. White, J. Personal communication. Potomac Electric
Power Company, Dickerson Power Plant, Dickerson, Mary-
land. March 1979.
27. Pugsley, J.M. 1979. Letter to Paul J. Rogoshewski,
Hittman Associates, Inc. Florida Power and Light
Company. January 18, 1979.
28. Schloffer, G. 1979. Personal communication. Baltimore
Gas and Electric Company, Riverside Power Station,
Turners Station, Maryland. March 21, 1979.
29. Schaper, F. 1979. Personal communication. Orange and
Rockland Utilities, Inc. Lovett Plant, Tomkins Cove,
New York. March 21, 1979.
30. EPA, 1974a. Development Document for Effluent Limita-
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for the Steam Electric Power Generating Point Source
Category. EPA 440/l-74-029a. U.S. Environmental
Protection Agency, Washington, DC. 524 pp.
31. EPA, 1976. 308 Data Portfolio (1976) on Riverside
Power Plant, Turners Station, Maryland. U.S. Environ-
mental Protection Agency, Washington, D.C.
32. Carr, R. 1979. Personal Communication. Florida Power
Corporation, St. Petersburg, Florida. November 27,
1979.
33. Hawaiian Electric Company, Inc. 1977. Letter to
Robert T. Brennan, Hittman Associates, Inc. April 4,
1977.
34. Pocock, 1976. A Treatability Study of Wastewater from
Coastal Power Generating Stations. Prepared for Southern
California Edison Company, Paramount, California. 16
pp. plus Appendix.
35. Cleland, J.G., and G.L. Kingsbury. 1977. Multimedia
Environmental Goals for Environmental Assessment,
Volume I, and Volume II, MEG Charts and Background
Information. U.S. Environmental Protection Agency.
EPA-600/7-77-136a and EPA-600/7-77-136b. 369 pp.
36. Jaywart, M. 1979. Personal communication. E.I.
DuPont de Nemours and Company. Wilmington, Delaware.
April 25, 1979.
37. Mace, G.R., and D. Casaburi. 1977. Lime Versus Caustic
for Neutralizing Power. Chemical Engineering Progress.
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101
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38. Cotton, F.A., and Wilkinson, G. 1966. Advanced In-
organic Chemistry: A Comprehensive Text. Interscience
Publishers, New York. 1136 pp.
39. Flaschka, H.A., and A.J. Barnard, Jr., eds. 1969.
Chelates in Analytical Chemistry. Marcel Dekker, Inc.,
New York.
40. Metcalf and Eddy, Inc. 1972. Wastewater Engineering:
Collection; Treatment; Disposal. McGraw-Hill Book
Company. New York. 782 pp.
41. Eckenfelder, W.W. 1966. Industrial Water Pollution
Control. McGraw-Hill Book Company, New York. 275 pp.
42. Gulp, R.L., G.M. Wesner, and G.L. Gulp. 1978. Hand-
book of Advanced Wastewater Treatment. Van Nostrand
Reinhold Company, New York. 632 pp.
43. Hittman Associates, Inc. 1978. Steam Electric Effluent
Guidelines Technical Report. H-C401-78-752D2. U.S.
Environmental Protection Agency, Washington, DC.
44. EPA. 308 Data Base - Steam Electric Power Plants.
Radian Corporation, McLean, Virginia.
45. Chu, T.J., R.J. Ruane, and G.R. Steiner. 1976. Char-
acteristics of Wastewater Discharges from Coal-Fired
Power Plants. Presented at the 31st Annual Purdue
Industrial Waste Conference, Purdue University, West
Lafayette, Indiana.
46. Mackenthun, K.M. 1973. Toward a Cleaner Aquatic
Environment. U.S. Environmental Protection Agency,
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pp.
102
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TECHNICAL REPORT DATA
(Please read Inunctions on the reverse before completing)
1. REPORT NO.
EPA-600/7-80-052
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Evaluation of Lime Precipitation for Treating Boiler
Tube Cleaning Wastes
5. REPORT DATE
March 1980
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
P. J. Rogoshewski and D.D. Carstea
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Hittman Associates, Inc.
9190 Red Branch Road
Columbia, Maryland 21045
10. PROGRAM ELEMENT NO.
INE624A
11. CONTRACT/GRANT NO.
68-02-2684
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 4/78-12/79
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES JERL-RTP project officer is Julian W. Jones, Mail Drop 61, 919/
541-2489. ' H , /
16. ABSTRACT
The report gives results of an evaluation of lime precipitation for treating
boiler tube cleaning wastes. In this project, wastewater samples were collected
from six boiler tubeside chemical cleanings, using complexing and chelating agents.
The samples represented: (1) ammoniacal bromate/hydrochloric acid, (2) thiourea-
hydrochloric acid, (3) hydroxyacetic-formic acid, (4) ammoniated citric acid, and
(5) ammoniated EDTA cleaning systems. Wastewater samples were also collected
from boiler fireside and air preheater washes. A treatment methodology was inves-
tigated that involved: dilution of the boiler tubeside cleaning wastewater with a mix-
ture of the fireside and air preheater wash wastewaters, precipitation with lime,
and addition of polymers for clarification. After settling of the solids, the superna-
tant was analyzed for total and dissolved iron, copper, nickel, zinc, and total sus-
pended solids. Major variations in testing included adjustments in pH and dilution
ratio. Results indicate that, on a bench scale, the treatment methodology effect-
ively reduced the concentration of iron, copper, and zinc in the tubeside cleaning
wastewater to < 1 mg/1. Attainable nickel residuals were also < 1 mg/1 for wastes
from all except the ammoniated EDTA system, for which nickel residuals were not
< 5 mg/1.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Pollution Precipitation
Boiler Tubes Evaluation
Chemical Cleaning Complex Compounds
Waste Water Chelation
Waste Treatment Polymers
Calcium Oxides
Pollution Control
Stationary Sources
13B 07D
13A 14B
13H,07A 07C
07B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
112
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
103
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