EPA/600/2-91/046
September 1991
BENCH-SCALE EVALUATION OF
AMMONIA REMOVAL FROM WASTEWATER
BY STEAM STRIPPING
by
G.B. Wickramanayake (Work Assignment Leader)
D. Evers, J.A. Kittel, and
A. Gavaskar
BATTELLE
Columbus Division
Columbus, Ohio 43201-2693
EPA Contract No. 68-03-3248
Project Officer
J. 0. Burckle
Water and Hazardous Waste Treatment Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
Cincinnati, Ohio 45268
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DISCLAIMER
This material has been funded wholly or in part by the United States
Environmental Protection Agency under contract 68-03-3248 to Battelle Memorial
Institute, Columbus Division. It has been subject to the Agency's review and
it has been approved for publication as an EPA document. Mention of trade
names or commercial products does not constitute endorsement or recommendation
for use.
i i
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Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased generation of
materials that, if improperly dealt with, can threaten both public health and
the environment. The U.S. Environmental Protection Agency is charged by Congress
with protecting the Nation's land, air, and water systems. Under a mandate of
national environmental laws, the Agency strives to formulate and implement
actions leading to a compatible balance between human activities and the ability
of natural systems to support and nurture life. These laws direct the EPA to
perform research to define our environmental problems, measure the impacts, and
search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning,
implementation, and management of research, development, and demonstration
programs to provide an authoritative, defensible engineering basis in support
of policies, programs, and regulations of the EPA with respect to drinking water,
wastewater, pesticides, toxic substances, solid and hazardous wastes, and
Superfund-related activities. This publication is one of the products of that
research and provides a vital communication link between the research and the
user community.
This work was requested by the Office of Water Regulations and Standards
for data to be developed on a bench-scale which would support the development
of a regulation for removal of ammonia from waste streams originating from the
extraction of metals, particularly tungsten, using ammoniacal lixivants.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
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ABSTRACT
The purpose of this study was to generate laboratory data to support the
development of discharge standards for ammonia in nonferrous metal winning
process wastewaters. The objective was accomplished by studying the removal
of ammonia from synthetically compounded "wastewater" samples using a
bench-scale steam stripping apparatus.
The analyses of estimated Henry's Law constant and changes in ammonia
solubilities indicate that addition of caustic, when compared with slaked
lime, can result in higher Henry's Law constants and lower solubilities for
the three waste streams studied. Although no significant variation of mass
transfer rate coefficient (K) was observed when S04= concentrations were
varied from 5,000 to 20,000 mg/L, K was highest for low S04* wastewaters when
pH was adjusted using NaOH.
The results of the steam stripping study indicated that the variation of
chemical constituents such as S0„- and the molal strength did not have a
significant effect on the efficiency of ammonia removal. Higher removals such
as 99.9 or more can be achieved by preheating wastewater and operating the
stripping tower at high steam to wastewater flowrates such as 4 lb/gallon.
The cost analysis based on the requirements for engineering unit processes and
operations indicated that lime can be more economical than caustic for pH
adjustment.
i v
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CONTENTS
Page
Foreword iii
Abstract iv
Figures vii
Tables ix
Acknowledgements xi
1. SUMMARY 1
1.1 INTRODUCTION 1
1.2 OBJECTIVES AND SCOPE
1.3 SUMMARY 1
1.3.1 Task 1: Theoretical and Laboratory Studies on the
Equilibrium and Mass Transfer of Ammonia
in Wastewater 1
1.3.2 Task 2: Ammonia Removal Studies Using Steam
Stripping Unit 2
1.3.3 Task 3: Engineering Cost Estimates 4
2. INTRODUCTION AND OBJECTIVES 5
2.1 INTRODUCTION . . 5
2.2 OVERALL PROJECT OBJECTIVES 5
3. TASK 1: THEORETICAL AND LABORATORY STUDIES
ON EQUILIBRIUM AND MASS-TRANSFER 7
3.1 OBJECTIVES AND SCOPE 7
3.2 METHODS 7
3.2.1 Laboratory Studies 7
3.2.1.1 Experimental Procedures ... 7
3.3 RESULTS AND DISCUSSION 9
3.3.1 Theoretical Studies on Ammonia/Water Equilibrium . 9
3.3.2 Laboratory Studies on Mass Transfer 16
3.4 SUMMARY 30
v
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CONTENTS
(continued)
Page
4. TASK 2: AMMONIA REMOVAL STUDIES USING
STEAM STRIPPING UNIT 33
4.1 OBJECTIVE AND SCOPE 33
4.2 DESIGN AND CONSTRUCTION OF THE STEAM STRIPPING UNIT ... 33
4.2.1 Characteristics of the Column 33
4.2.1.1 Flow-Mode 33
4.2.1.2 Column Packing 34
4.2.1.3 Column Material 34
4.2.2 Design of the Stripping Unit 35
4.2.2.1 Henry's Law Constant 35
4.2.2.2 Number of Transfer Units 35
4.2.2.3 Diameter of the Column . 36
4.2.2.4 Height Equivalent to a Transfer Unit ... 40
4.2.3 Scale-Up 40
4.3 EXPERIMENTAL PROCEDURES 41
4.4 RESULTS AND DISCUSSION 50
4.5 SUMMARY AND CONCLUSIONS 60
5. ENGINEERING COST ESTIMATES 62
5.1 OBJECTIVE AND SCOPE 62
5.2 METHODS 67
5.2.1 Equilibria Modelling 67
5.2.2 Cost Estimates 67
5.2.3 Process Design 73
5.3 RESULTS AND DISCUSSION 75
5.4 SUMMARY AND CONCLUSIONS 83
6. QUALITY ASSURANCE/QUALITY CONTROL 84
7. REFERENCES . ! 86
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FIGURES
FIGURE Paoe
3.1 Variation of anvnonia concentration with time: Wastewater A
and NaOH 24
3.2 Variation of ammonia concentration with time: Wastewater A
and Ca(0H)2 25
3.3 Variation of ammonia concentration with time: Wastewater B
and NaOH 26
3.4 Variation of ammonia concentration with time: Wastewater B
and Ca(0H)2 27
3.5 Variation of ammonia concentration with time: Wastewater C
and NaOH 28
3.6 Variation of ammonia concentration with time: Wastewater C
and Ca(0H)2 29
4.1 Dependence of NTU on removal efficiency and stripping factor . . . 37
4.2 Generalized correlation for flooding and pressure drop in
packed columns 38
4.3 Flowrates and packing size 44
4.4 Stripping factors and height of column 46
4.5 Experimental set up for ammonia removal by steam stripping. . 48
4.6 Calibration of steam flow rate across the orifice 49
5.1 Calculated pH for Plants 1, 2, 3, and 5 for lime addition. . . 68
5.2 Calculated pH for Plants 1, 2, 3, and 5 for sodium hydroxide
addition 69
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FIGURES
(continued)
FIGURE Page
5.3 Calculated sludge production for Plants 1, 2, 3, and 5 for
lime addition 70
5.4 Calculated sludge production for Plants 1, 2, 3, and 5 for
sodium hydroxide addition 71
vi i i
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TABLES
IMLE M
1.1 SUMMARY RESULTS OF LABORATORY STUDY ON STEAM STRIPPING .... 3
3.1 WASTEWATER CHARACTERISTICS FOR GAS TRANSFER RATE EXPERIMENTS . 8
3.2 REPORTED VALUES FOR h+ AND h. 12
3.3 CHEMICAL CHARACTERISTICS OF SYNTHETIC WASTEWATER USED IN
MASS-TRANSFER STUDIES 13
3.4 ESTIMATES OF HENRY'S LAW CONSTANT FOR SYNTHETIC WASTEWATER . . 14
3.5 RESULTS OF MASS-TRANSFER EXPERIMENT A-NaOH 17
3.6 RESULTS OF MASS-TRANSFER EXPERIMENT A-Ca(OH)2 . 18
3.7 RESULTS OF MASS-TRANSFER EXPERIMENT B-NaOH 19
3.8 RESULTS OF MASS-TRANSFER EXPERIMENT B-Ca(OH)2 20
3.9 RESULTS OF MASS-TRANSFER EXPERIMENT C-NaOH 21
3.10 RESULTS OF MASS-TRANSFER EXPERIMENT C-Ca(OH)2 22
3.11 MASS TRANSFER RATE COEFFICIENTS FOR AMMONIA IN DIFFERENT
WASTE STREAMS 31
4.1 COLUMN DIAMETER FOR 1/2-INCH PACKING AND R=5 42
4.2 EFFECT OF PACKING SIZE 43
4.3 DIMENSIONS OF THE COLUMN FOR VARIOUS VALUES OF R FOR
5/8-INCH PACKING 45
4.4 RESULTS FOR PILOT RUN NO. P-l FOR WASTEWATER B AND NaOH ... 51
4.5 RESULTS FOR PILOT RUN NO. P-2 FOR WASTEWATER B AND NaOH ... 52
4.6 RESULTS FOR PILOT RUN NO. P-3 FOR WASTEWATER B AND CaO . . . . 53
ix
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TABLES
(continued)
TABLE Page
4.7 RESULTS FOR PILOT RUN NO. P-4 FOR WASTEWATER B AND CaO . . . . 54
4.8 RESULTS FOR PILOT RUN NO. P-5 FOR WASTEWATER C AND NaOH ... 55
4.9 RESULTS FOR PILOT RUN NO. P-6 FOR WASTEWATER C AND NaOH ... 56
4.10 RESULTS FOR PILOT RUN NO. P-7 FOR WASTEWATER C AND NaOH ... 57
4.11 RESULTS FOR PILOT RUN NO. P-8 FOR WASTEWATER C AND CaO ... . 58
4.12 RESULTS FOR PILOT RUN NO. P-9 FOR WASTEWATER C AND CaO ... . 59
4.13 SUMMARY RESULTS OF LABORATORY STUDY ON STEAM STRIPPING .... 61
5.1 CHEMICAL AND PHYSICAL CHARACTERISTICS OF METAL PROCESSING
WASTEWATERS CONTAINING AMMONIA: CONCENTRATION IN mg/L .... 63
5.2 CHARACTERISTICS OF REPRESENTATIVE WASTEWATER STREAMS 66
5.3 SUMMARY OF CHEMICAL AND SLUDGE DATA 72
5.4 ASSUMED CONSTANT VALUES 74
5.5 DESIGN EQUATIONS 76
5.6 CONVERSION FACTORS 77
5.7 SUMMARY OF COST ESTIMATES FOR PLANT 1 78
5.8 SUMMARY OF COST ESTIMATES FOR PLANT 2 79
5.9 SUMMARY OF COST ESTIMATES FOR PLANT 3 . . 80
5.10 SUMMARY OF COST ESTIMATES FOR PLANT 5 81
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-«¦
ACKNOWLEDGEMENTS
Battelle Columbus Division (BCD) prepared this document for the Risk
Reduction Engineering Laboratory (RREL), U.S. Environmental Protection Agency
(U.S. EPA). Numerous people contributed to the research and writing of this
report. The authors wish to thank these individuals for their contributions.
John 0. Burckle, U.S. EPA Project Officer, and Jeff Means, BCD Project
Manager, in particular, are gratefully acknowledged for their direction and
support. Ron Clark of BCD also contributed significantly at the initiation of
this project. Ernie Hall of U.S. EPA is acknowledged for providing guidance
and required additional information. Greg Headington, Larry Smith, and E.
Voudrias of BCD are thanked for their assistance during this study, Robert
Hinchee for technical review, Tom Bigelow for editorial assistance, and Cleta
Richey for text processing support.
xi
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1. SUMMARY
1.1 INTRODUCTION
Some industrial wastewaters, such as nonferrous metal industry
wastewaters, are high in dissolved solids (e.g., 140,000 ppm total dissolved
solids) and ammonia (e.g., 22,000 mg/L). These wastewaters require treatment
for removal of the ammonia, as well as the dissolved solids, to meet the
discharge standards. The practical methods of removing airanonia-nitrogen from
wastewaters include biological nitrification-denitrification, breakpoint
chlorination, evaporation, reverse osmosis, ion exchange, air stripping, and
steam stripping. The purpose of this study was to generate data to support
the development for the limitation of the discharge standards for the ammonia
content of wastewaters from certain nonferrous metal smelting and refining
processe by employing steam stripping, which is an effective ammonia removal
and recovery method.
1.2 OBJECTIVES AND SCOPE
The overall objective, which was to generate laboratory data to support
the development of effluent standards for high-strength ammonia wastewaters,
was pursued as three discrete tasks. Task 1 involved performing theoretical
and laboratory studies to determine the effects of wastewater composition on
the equilibrium of ammonia (gas) and water and gas-liquid mass transfer rates,
especially within the temperature range of interest in actual plant operation.
In Task 2, laboratory tests were performed using a bench-scale steam stripping
apparatus. Experiments were conducted using two representative synthetic
wastewaters; pH adjustment was accomplished using lime and caustic. Task 3
involved analysis and estimation of capital and operating costs of the pH
adjustment methods, and of the handling and disposal of waste sludge.
1.3 SUMMARY
1.3.1 Task I: Theoretical and Laboratory Studies on the Equilibrium and
Mass Transfer of Ammonia in Wastewater
The analyses of the estimated Henry's Law constant and changes in
solubilities of ammonia indicate that addition of caustic, compared with
slaked lime, can result in higher Henry's Law constants and ammonia lower
1
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solubilities for the three waste streams considered. These effects can be
attributed to the relatively high ionic strength resulting in wastewaters when
pH was adjusted with NaOH. Between solutions B and C, where the sulfate
concentration was varied without changing the solution strength (total number
of moles), no significant difference in Henry's Law constant or solubility
could be seen for either of the two pH adjustment methods. The highest
Henry's Law constant and corresponding lowest ammonia solubility were observed
in solution A which has the highest molal strength.
Experimental studies to determine the effects of dissolved species and pH
adjustment method on the mass transfer rate coefficient (K) indicate that
those effects are relatively low and the maximum changes in mass transfer rate
coefficient do not exceed 25 percent. In two of the three different
solutions, however, the mass transfer rate coefficients were higher for the
waste stream where pH was adjusted using caustic. For solutions with
approximately the same S04~ concentration but different molal strength, the
mass transfer rate coefficients were comparable when NaOH was used as the pH
adjustment method. For Ca(0H)2, however, the K values were comparable for
those where both the molal strength and S04" level were different. The
overall analysis of data indicate that, when compared with lime, addition of
NaOH can promote the ammonia removal for solutions with relatively low S04=
levels (5,000 mg/L).
1.3.2 Task 2: Ammonia Removal Studies Using Steam Stripping Unit
The results of the steam stripping study are summarized in Table 1.1.
Data show that when the steam to wastewater ratios are low (1.3 lb/gal), the
ammonia removal efficiency was as low as 93 percent. By increasing the steam
to wastewater ratio to 3.8 lb/gal, removals of over 99.9 percent have been
observed. The removal efficiency in one study was improved by 2 percentile
points when the temperature of influent waste stream was raised by about 20°C.
The addition of.lime resulted in more than a 10°C increase in temperature
since the hydration of lime is an exothermic process.
2
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TABLE 1.1. SUMMARY RESULTS OF LABORATORY STUDY ON STEAM STRIPPING
Wastewater
pH
Adjustment
Method
Wastewater Temp. °C
Column
Influent
Column
Effluent
Steam to
Wastewater Ratio
(lb/gallon)
.NH3-N com:., »fl/L ^
Influent Effluent Removal, %
B (low SO4)
C (high SO4)
NaOH
26
101
1.9
5,200
32-102
99.1
NaOH
26
101
1.3
5,200
255-420
93.1
CaO
38
101
1.9
5,100
188-288
95.3
CaO
39
101
3.B
5,000
12-16
99.7
NaOH
26
101
1.9
4,750
121-198
96.9
NaOH
26
101
3.B
4,700
3.9-4.5
99.91
NaON
47
101
1.9
3,950
2.0-80
98.8
CaO
39
101
1.9
3,950
87-92
97.7
CaO
39
101
3.8
3,825
1.1-2.2
99.96
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For wastewater with low initial S04= level (5,000 mg/L), ammonia removal
was 3 percent higher when pH was adjusted with caustic rather than lime.
These observations agree with the trends predicted from the estimated Henry's
Law constant and mass transfer rate coefficient. In the experiments conducted
with wastewaters using higher initial S04~ levels (20,000 mg/L), ammonia
removal was slightly higher when pH was adjusted with lime instead of caustic.
These observations agree with the conclusions reached from the corresponding
mass transfer rate studies, which did not agree with the theoretical estimates
of solubilities based on Henry's Law constant.
In summary, more than 99.9 percent removal of ammonia can be achieved by
introducing high steam to wastewater ratios such as 3.8 lb/gallon. Variation
of chemical constituents such as S04~ and the molal strength have only a
little effect on net NH3 removal. Higher removal efficiencies can be achieved
by preheating wastewaters and operating the stripping tower at high
temperatures by increasing steam to wastewater ratios.
1.3.3 Task 3: Engineering Cost Estimates
Cost estimates for the chemicals and equipment to adjust the pH of an
ammonia-bearing, metal-winning wastewater prior to stripping show that lime
can be more economical than caustic for pH adjustment. In addition, the most
cost-effective method for disposal of the sludge solids generated is
dewatering in a lagoon followed by landfill disposal of the solids. However,
there may be a different set of cost-effective processes when costs for land,
transport, and handling of large quantities of sludge are high.
4
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2. INTRODUCTION AND OBJECTIVES
2.1 INTRODUCTION
Extracting metal values from some ores requires the use of
hydrometallurgical techniques which employ ammoniacal lixiviants. The metal
values are recovered from the pregnant liquors, leaving an aqueous wastewater
that is high in dissolved solids and ammonia. This wastewater requires
treatment for removal of the ammonia as well as the dissolved solids, to meet
the discharge standards required under the Effluent Guidelines for the
nonferrous metals industry.
The practical methods of removing ammonia-nitrogen from wastewaters
include biological nitrification-denitrification, breakpoint chlorination,
evaporation, reverse osmosis, ion exchange, air stripping, and steam stripping
(Struzeski, 1978). The present study focused on steam stripping, which is
also being identified as a very effective ammonia removal method for the metal
smelting and refining industry (USEPA, 1976). The purpose of this work
assignment was to generate data to support the development of discharge
standards for such wastewaters by employing the steam stripping technique.
2.2 OVERALL PROJECT OBJECTIVES
The purpose of this project was to generate laboratory data to support
the development of discharge standards for ammonia in nonferrous metal winning
process wastewaters. The objective was accomplished by studying the removal
of ammonia from synthetically compounded "wastewater" samples using a
bench-scale steam stripping apparatus.
This overall objective was pursued as three discrete tasks. Task 1
involved performing theoretical and laboratory studies to determine the
effects of wastewater composition on the equilibrium of ammonia (gas) and
water and gas-liquid mass transfer rates, within the temperature range of
interest in actual plant operation. In Task 2, laboratory tests were
performed using a bench-scale steam stripping apparatus. Experiments were
conducted using two representative synthetic wastewaters; pH adjustment was
5
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accomplished using lime and caustic. Task 3 involved analysis and estimation
of capital and operating costs of the pH adjustment methods, and of the
handling and disposal of waste sludge.
6
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3. TASK 1: THEORETICAL AND LABORATORY STUDIES
ON EQUILIBRIUM AND MASS-TRANSFER
3.1 OBJECTIVES AND SCOPE
One of the objectives of this task was to investigate how the distribu-
tion of inorganic species and changes in temperature affect the equilibrium of
ammonia (gas) and the wastewaters. Effects of different electrolytes, such as
Na+, Mg**, Ca"^, S0~4, and CI", on the Henry's Law constant (He) were
evaluated.
The second part of Task 1 involved conducting laboratory experiments to
determine how the differences in wastewater characteristics would affect the
overall gas-liquid mass transfer rates. These experiments were conducted in
identical completely mixed batch reactors at temperatures near 90°C.
3.2 METHODS
3.2.1 Laboratory Studies
The second part of Task 1 involved experiments to study the effect of
varying S04~ concentration, molal strength, and pH adjustment method [NaOH or
Ca(0H)2] on the gas transfer rates for ammonia. These characteristics of the
synthetic wastewaters that were used in this study are given in Table 3.1.
Waste stream A was designed to have a high S04~ level and a high total molal
strength. Waste stream B has a lower S04~ level than A, whereas both A and C
have the same S04~ level. Waste streams B and C have the same molal strength
and were brought to such conditions by adjusting CI" concentrations.
3.2.1.1 Experimental Procedures--
The gas mass transfer experiments were conducted using 1.5-L samples.
The batch reactor was a 2-L beaker placed in a constant temperature hot-water
bath. Heated synthetic wastewater was first added to the reactor. Then a
predetermined amount of either heated NaOH solution (10 N) or Ca(0H)2 powder
was added to the wastewater sample. The amount of base required to raise the
pH to 12 was determined by mixing an aliquot of wastewater with the base at
room temperature. For the mass transfer experiments, the base was added at
elevated temperatures, otherwise, if the pH was raised first, a significant
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TABLE 3.1. WASTEWATER CHARACTERISTICS SELECTED FOR MASS
TRANSFER RATE EXPERIMENTS
Chemical Species
Concentration, mq/L
Wastewater A
Wastewater B
Wastewater C
NH3-N
5,000
5,000
5,000
Mg*4"
200
200
200
Na+
19,127
11,939
11,939
SO4
20,000
5,000
20,000
CI'
28,000
28,000
16,905
TDS
72,127
50,139
54,045
8
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fraction of ammonia can be lost during the heating process. A sample was
withdrawn from the reactor, for pH and chemical analyses, prior to initiating
the test. Then an aliquot of 1 mL was taken at regular time intervals for
ammonia analysis. These samples were immediately dispensed to volumetric
flasks containing 99 mL of diluted HC1 at room temperature. The acid
treatment was performed to convert ammonia to anvnonium ion, thus avoiding
further loss of ammonia. All ammonia analyses were performed using an ion
specific electrode (Orion 95-12 anmonia probe and Orion 701A Ionalyzer).
The contents in the reactor were continuously mixed using a mechanical
stirrer rotating at a constant speed. The temperature in the water bath was
kept at 90°C. The corresponding reactor temperature was approximately 88°C.
Temperatures typical for ammonia stripping units are higher than these values
(approximately 100°C), but such temperatures are not feasible in the mass
transfer experiments because of the rapid loss of reactor contents by
evaporation.
The wastewaters were analyzed for sodium, magnesium, calcium, sulphate,
and chloride before and after the pH adjustment. If the final wastewater pH
was found to vary beyond 10 percent of its starting value, the experiments
were repeated.
3.3 RESULTS AND DISCUSSION
3.3.1 Theoretical Studies on Ammonia/Mater Equilibrium
The solubility of ammonia in water depends on the partial pressure of
ammonia in gaseous phase, temperature, and the distribution of dissolved
species in the aqueous system. The dependency of solubility on partial
pressure can be expressed as:
P = He C (1)
where
p = partial pressure of amnonia
C = ammonia concentration in water
He = Henry's Law constant.
The Henry's Law constant is an increasing function of temperature as
given in the following equation (Danckwerts, 1970):
9
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where
T - absolute temperature
R - gas constant
H - heat of absorption of the gas.
Wastewaters from the nonferrous metals industry contain a variety of
electrolytes. Distribution of these electrolytes affects the solubility of
NH3 and, thus, the Henry's Law constant. The relationship between the ionic
strength (I) and He is given by (Danckwerts, 1970):
loQlO (H,/Heo) - hi (3)
where
Heo = Henry's Law constant for water
h = Setchenow constant
I - ionic strength.
The ionic strength of the solution is given by
I = \ 2 C.Z.2 (4)
where Ci is the concentration of ions of valency Zj.
The Setchenow constant is the sum of contributions of the positively (hj
and negatively (hj charged ionic species and the gaseous (h5) species in
solution.
h = h+ + h. + hG (5)
Some reported values for h,. and h_ are given in Table 3.2. These values
reported by Barrett (1966) and Onda et al. (1970) agreed well for most of the
species.
10
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In mixed electrolytes, it may be supposed that the value of He will be
given by an expression of the form (Danckwerts, 1970):
logjo (He/Heo) = hjlj + h2I2 + .... (6)
where I, is the ionic strength attributable to species of electrolyte No. 1
and h, is the Setchenow constant for that electrolyte. Based on Equation 6,
the Henry's Law constant can be estimated for the solutions with different
composition.
Analytical results of the synthetic wastewaters (A, B, and C) used in
this study are given in Table 3.3. Using these data and Equations 4, 5, and
6, the Hg/HgO were calculated. The estimated Hg/HgO values are given in
Table 3.4. The h+ and h_ for corresponding species were obtained from Barrett
(1966) as given in Table 3.2. The value of hG used in Equation 5 is -0.054
liters per gram ion at 25°C (Danckwerts, 1970).
Since the reciprocal of He can be used to compare the change in
solubility of ammonia, the results presented in Table 3.4 indicates how the
different wastewaters affect the solubility of NH3 when pH was adjusted by
either NaOH or Ca(0H)2. When compared to Ca(0H)2, addition of NaOH to adjust
the wastewater pH resulted in relatively low solubility of NH3 in wastewater.
This can be attributed to the relatively high ionic strength resulting in
wastewater when pH was adjusted with NaOH. Overall, change in S0~4
concentration does not appear to have a significant effect on the Henry's Law
constant. Between solutions B and C where the sulfate concentration was
varied without changing the solution strength (total number of moles), no
significant difference in Henry's Law constant or solubility could be seen for
either of the two pH adjustment methods. Highest He values and corresponding
lowest in ammonia solubility was observed in solution A which has the highest
molal strength.
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TABLE 3.2. REPORTED VALUES FOR h+ AND h.
h+ (L/Q-ion) h- (L/g-ion)
Solute Barrett Onda et al. Solute Barrett Onda et al.
(1966) (1970) (1966) (1970)
H+
0.000
-0.0017
F"
-
-
Li*
-
0.0677
CI"
0.021
0.021
Na*
0.091
0.091
Br"
0.012
0.0104
K*
0.074
0.0731
I"
0.005
-0.0082
Rb+
-
0.0644
soy
0.022
0.0240
Cs+
-
0.0509
NO3
-0.001
0.0024
Mg**
0.051
0.0525
co--
0.021
0.0548
Ca**
0.053
0.0546
OH"
0.066
0.0669
Sr**
-
0.0648
CNS"
-
-0.0594
Ba**
0.060
0.0620
~r
-
0.0059
Cr***
-
0.0107
so^
-
0.0069
Mn**
0.046
0.0468
HSO5
-
0.0663
Fe**
0.049
0.0491
HS"
-
0.0512
Co**
0.058
0.0559
cio J
-
-
Ni**
0.059
0.0573
^ ++
Cu
-
-
Zn**
0.048
0.0503
Cd**
-
0.1011
Al***
-
0.0367
nhJ
0.028
0.0356
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TABLE 3.3. CHEMICAL CHARACTERISTICS OF SYNTHETIC WASTEWATER
USED IN MASS-TRANSFER STUDIES
Concentration, tnq/L
Sample
Sulfate
Chloride
Magnesium
Sodium
Calcium
A [initial]
A [initial]
(duplicate)
A [pH adjusted
with NaOH]
22,000
25,500
19,000
28,000
27,750
30,500
184
180
<10
19,000
20,000
31,000
<10
<10
<10
A [initial]
A [pH adjusted
with Ca(0H)2]
66,000a
5,300
27,500
31,500
365
<10
19,000 .
21,000
<10
1,500
B [initial]
B [pH adjusted
with NaOH]
8,200
6,500
28,750
29,500
184
<10
17,500
24,000
<10
<10
B [initial
B [pH adjusted
with Ca(0H)2]
8,200
<4
28,750
29,500
184
<10
17,500
15,000
<10
5,000
C [initial]
C [pH adjusted
with NaOH]
24,033
25,000
20,376
975b
193
<10
17,764
24,000
<10
<10
C [initial]
C [pH adjusted
with Ca(0H)2]
24,000
5,500
17,750
19,500
181
<10
13,000
14,000
<10
1,100
Distilled Water
[control]
<4
<50
<10
11
<10
a Error in analytical results. For He calculations 22,000 mg/L was used,
b Error in analytical results. For He calculations 19,500 mg/L was used.
13
-------
TABLE 3.4. ESTIMATES OF HENRY'S LAW CONSTANT FOR SYNTHETIC WASTEWATER
% Decrease
Concentration h(c) l(d) In NH3
Sample(a) Electrolyte M(b) 1/g ion g ion/L Ihl(e) He/Heo(f) He(9) solubility(h)
A/NaOH
A/Ca(OH)2
B/NaOH
B/Ca(OH)2
NaOH
Na?S04
NaCl
NaCl
Na2S04
CaCl2
NaCl
Na2S04
NaOH
NaCl
CaCl2
Ca(0H)2
0.093
0.I9B
0.859
0-812
0.055
0.038
0.831
0.067'
0.079
0.652
0.089
0.036
0.103
0.059
0.058
0.058
0.059
0.02
0.058
0.059
0.103
0.058
0.02
0.065
0.093
0.594
0.859
0.812
0.165
0.057
0.831
0.201
0.079
0.652
0.131
0.054
0.0944 1.24 8.6x10-4 19
0.0578 1.14 7.9X10-4 12
0.0682 1.17 8.13x10-4 15
0.044 1.11 7.7x10-4 10
-------
TABLE 3.4. (continued)
JU flprrp3cp
Concentration h(c) l(<0 in NH3
Sample(a) Electrolyte M(b) 1/g ion g ion/L Ihl(e) He/Heo(0 He(9) solubility(h)
C/NaOH
NaCl
Na2S04
0.053
0.260
0.058
0.059
0.563
0.78
0.0787
1.20
8.3x10-4
17
C/Ca(0H)2
NaCl
Na2S04
CaS04
0.549
0.029
0.028
0.058
0.059
0.021
0.549
0.087
0.07
0.0318
1.09
7.6x10-4
8
(a) Solution and the pH adjustment method [NaOH or Ca(0H)2] are indicated.
(b) Concentration estimated from data given in Table 3.3.
(c) Estimated using Equation 5 and data given 1n Table 3.2 (Barrett, 1966)
hg = -0.054 (Danckwerts, 1970).
(d) Ionic strength estimated using Equation 4.
(e) Summation of hi values for all electrolytes.
(0 Estimated from Equation 6.
(g) Assuming Heo = 6.95x10-4 at 25°C (Powers, 1987).
(h) Percent decrease is with respect to NH3 solubility in pure water.
-------
3.3.2 Laboratory Studies on Mass Transfer
A number of experiments were conducted in order to estimate the rate of
transfer of arranonia from solution. These studies were conducted with
synthetic, ammonia-bearing wastewaters of known composition. The composition
of the wastewaters was restricted to three cations, NH+4, Mg++, Na+, and two
anions, S04= and CI". The relative proportions of these ions were adjusted to
provide solutions of constant NH3-N concentration but varying ionic strength.
Solutions were adjusted to pH 12 or greater with slaked lime (Ca(0H)2) or
sodium hydroxide (NaOH). The high pH promotes dissociation of NH4+ to NH3.
The wastewater compositions along with the chemical used for pH adjustment are
summarized in Tables 3.5 through 3.10. Also given in these tables are NH3-N
concentrations measured during the course of each mass transfer experiment.
These values were normalized by dividing each by the initial NH3-N.
concentration, Cc. Further manipulation consisted of calculating the natural
logarithm of each normalized value. The natural logarithm of the normalized
values is also compiled in the tables and was used to determine the overall
mass transfer rate coefficient.
The rate at which the NH3-N concentration decreases in solution can be
expressed by the following first order differential equation:
31 " K <7>
where
C = NH3-N concentration at time t
Cs = equilibrium NH3-N concentration
K = overall mass transfer rate coefficient.
The solution to this equation is
where C0 = initial NH3-N concentration. Since the NH3-N concentration in the
atmosphere can be assumed to be approximately 0, Cs can be assumed to be 0 by
Henry's Law.
16
-------
TABLE 3.5. RESULTS OF MASS-TRANSFER EXPERIMENT A-NaOH
Wastewater Composition Solution A
Concentration. mq/L
cations initial after pH adjustment
NH4 5,000 4,250 (Reported as nitrogen)
Mg2+ 184 <10
Na+ 19,000 31,000
anions
SO*" 22,000 19,000
CI' 28,000 30,500
Solution pH = 12.01
Temperature (°C) = 86.3
pH adjustment with NaOH
Time (min) NH3-N (mg/L) In (C/C0)
0 4,250 0
2 4,100 -0.0359
4 4,050 -0.0482
6 4,000 -0.0606
8 3,850 -0.0988
10 3,750 -0.125
12 3,650 -0.152
14 3,550 -0.180
16 3,450 -0.209
18 3,400 -0.213
21 3,350 -0.238
24 3,100 -0.316
27 2,950 -0.365
30 2,700 -0.454
33 2,650 -0.472
36 2,550 -0.511
41 2,350 -0.593
46 2,200 -0.659
51 1,950 -0.779
56 1,850 -0.832
17
-------
TABLE 3.6. RESULTS OF MASS-TRANSFER EXPERIMENT A-Ca(OH)2
Wastewater Composition Solution A
Concentration, mq/L
cations
initial
after pH adjustment
NH4
5,000
3,600
Mg2+
365
<10
Na+
19,000
21,000
anions
SO4"
66,000
5,300
CI"
27,500
31,500
(Reported as nitrogen)
Solution pH = 11.90
Temperature (°C) = 88.2
pH adjustment with Ca(0H)2
Time (min)
0
2
4
6
8
10
13
16
19
22
25
30
35
40
45
50
55
60
NH3-N (mg/L)
3,600
3,450
3,400
3,250
3,100
3,050
2,950
2,800
2,650
2,550
2,500
2,300
2,200
2,000
1,900
1,750
1,650
1,600
In (C/C0)
0
-0.043
-0.057
-0.102
-0.150
-0.166
-0.199
-0.251
-0.306
-0.345
-0.365
-0.448
-0.492
-0.588
-0.639
-0.721
-0.780
-0.811
18
-------
TABLE 3.7. RESULTS OF MASS-TRANSFER EXPERIMENT B-NaOH
Wastewater Composition Solution B
Concentration. mq/L
cations initial after pH adjustment
NH4 5,000 4,150 (Reported as nitrogen)
Mg2+ 184 <10
Na+ 17,500 24,000
anions
SO^" 8,200 6,500
CI' 28,750 29,500
Solution pH = 11.93
Temperature (°C) = 88.6
pH adjustment with NaOH
Time (min) NH3-N (mg/L) In (C/Co)
0 4,150 0
2 3,850 -0.0750
4 3,650 -0.128
6 3,550 -0.156
8 3,450 -0.185
10 3,350 -0.214
13 3,250 -0.244
16 3,100 -0.292
19 2,900 -0.358
22 2,700 -0.430
25 2,600 -0.468
33 2,200 -0.635
38 2,000 -0.730
43 1,850 -0.808
48 1,650 -0.922
53 1,500 -1.018
58 1,300 -1.161
19
-------
TABLE 3.8. RESULTS OF MASS-TRANSFER EXPERIMENT B-Ca(OH)2
Wastewater Composition
Solution B
Concentration, mq/L
cations
initial
after pH adjustment
NH4
5,000
3,450 (Reported
as nitrogen)
Mg2+ .
184
<10
Na+
17,500
15,000
anions
S04"
8,200
<4
cr
28,750
29,500
Solution pH
= 11.63
Temperature (°C)
= 89
pH adjustment wi
th Ca(0H)2
Time (min)
NH3-N (mg/L)
In (C/C0)
0
3,450
0
2
3,200
-0.0753
4
3,150
-0.0910
6
3,100
-0.107
8
2,950
-0.157
10
2,850
-0.191
13
2,750
-0.227
16
2,650
-0.264
19
2,500
-0.322
22
2,250
-0.427
25
2,100
-0.496
30
2,050
-0.521
35
1,950
-0.571
40
1,800
-0.651
45
1,650
-0.738
50
1,550
-0.800
55
1,500
-0.833
60
1,400
-0.902
20
-------
TABLE 3.9. RESULTS OF MASS-TRANSFER EXPERIMENT C-NaOH
Wastewater Composition
Solution C
cations
NH4
Mg2+
Na+
anions
SO.
C V
2-
Concentration. tnq/L
initial after pH adjustment
5,000
193
17,700
24,000
20,300
3,950
<10
24,000
25,000
975
(Reported as nitrogen)
Solution pH = 12.13
Temperature (°C) = 88.7
pH adjustment with NaOH
Time (min)
NH3-N (mg/L)
In (C/C0)
0
3,950
0
2
3,650
-0.0789
4
3,600
-0.0928
6
3,450
-0.135
8
3,250
-0.195
10
3,150
-0.226
13
3,150
-0.226
16
2,900
-0.309
19
2,800
-0.344
22
2,500
-0.457
25
2,550
-0.438
30
2,300
-0.541
35
2,050
-0.656
40
2,000
-0.681
45
1,800
-0.786
50
1,650
-0.873
55
1,550
-0.936
60
1,400
-1.037
21
-------
TABLE 3.10. RESULTS OF MASS-TRANSFER EXPERIMENT C-Ca(0H)2
Wastewater Composition
Solution C
Concentration, mg/L
cations
initial
after pH adjustment
NH4
5,000
3,250 (Reported
Mg2+
181
<10
Na+
13,000
14,000
anions
$°4~
24,000
5,500
cr
17,750
19,500
Solution pH
= 12.18
Temperature (°C)
¦= 88.8
pH adjustment with Ca(OH)2
Time (min)
NH3-N (mg/L)
0
2
4
6
8
10
13
16
19
22
25
30
35
40
45
50
55
60
3,250
2,950
2,750
2,700
2,650
2,500
2,400
2,300
2,200
2,100
1,950
1,800
1,650
1,500
1,400
1,250
1,200
1,100
In (C/C0)
0
-0.0968
-0.167
-0.185
-0.204
-0.262
-0.303
-0.346
-0.390
-0.437
-0.511
-0.591
-0.678
-0.773
-0.842
-0.956
-0.996
-1.083
22
-------
P = H Cs
(9)
where
p = partial pressure of NH3-N in atmosphere
H = Henry's Law constant.
Therefore Equation 8 can be simplified to the following form:
(10)
or by calculating the natural logarithm of each side to linearize the equation
Figures 3.1 through 3.6 show the results plotted according to Equation 11.
It is apparent from Figures 3.1 through 3.6 that the data do not follow a
first order rate law across the time span given. However, the curves consist
of an initial shoulder followed by a linear portion. The overall mass
transfer rate coefficients were determined by applying linear regression to
the straight portion of the curve. The straight portion of the curve was
generally found to be that portion of the graph that began at a point
corresponding to an NH3-N concentration of 2500 mg/L and continuing to lower
concentrations. The estimated mass transfer rate coefficients are given in
Table 3.11.
The nonlinearity of the data can best be explained as experimental
limitations. At high NH3-N concentrations the partial pressure of NH3-N
above the reactors was not necessarily zero due to limitations in the ability
to move gas away from the liquid surface. As NH3-N gas accumulates over the
liquid, the equilibrium concentration, Cs, increases. Since the calculations
were performed assuming Cs = 0, the data were not expected to be linear until
the partial pressure exerted by ammonia is zero.
ln(C/C0) « -Kt
(11)
23
-------
0.0 -»
-0.1
-0.2 -
-0.3 -
-0.4 -
-0.5 -
-0.6 -
-0.7 -
-0.8 -
-0.9
56
0 2 4 6 8
12
33 36 41 46
16 18 21 24 27
time, mln.
Figure 3.1. Variation of ammonia concentration with time: Wastewater A and NaOH.
-------
-0.1
-0.2 -
-0.3 -
-0.4 -
-0.5 -
-0.6 -
-0.7 -
—0.8 -
-0.9
B 10 13 16 19 22 25 30 35 40 45 50 55 60
4
6
0
time, mln.
Figure 3.2. Variation of ammonia concentration with time: Wastewater A and Ca(0H)?.
-------
o.o -m
-0.1
-0.2 -
-0.3 -
-0.4 -
-0.5 -
-0.6 -
-0.7 -
-0.8 -
-0.9 -
-1.0 -
-1.1
-1.2
43 48 53 58
8
22 25 33
time, mln.
Figure 3.3. Variation of ammonia concentration with time: Wastewater B and NaOH.
-------
0.0 -o
-0.1
-0.2 -
—0.3 -
-0.5 -
-0.6 -
-0.7 -
-0.8 -
-0.9 -
-1.0
2
8 10 13 16
22 25
4
40
60
6
time, mln.
Figure 3.4. Variation of ammonia concentration with time: Wastewater B and Ca(0H)?.
-------
0.0 -»
0.2 -
0.3 -
0.4 -
0.5 -
0.6 -
0.7 -
0.0 -
1.0 -
50 55 60
time, mln.
Figure 3.5. Variation of ammonia concentration with time: Wastewater C and NaOH.
-------
0.0 -&
0.2 -
0.3 -
0.4 -
0.5 ~
0.7 -
0.8 -
0.9 -
40 45 50 55 60
10 13 16 19 22
30
time, mln.
Figure 3.6. Variation of ammonia concentration with time: Wastewater C and Ca(0H)2.
-------
As can be seen in the Table 3.11, the mass transfer rate coefficient does
not vary significantly with both solution composition and the base used for pH
adjustment. In two of the three cases, however, the mass transfer rate
coefficient was higher for the waste stream where pH was adjusted using NaOH.
Also, for solutions A and C where the initial S04~ concentrations were
approximately the same, the mass transfer rate coefficients were also
comparable. Solution B with the lowest S04* concentration appeared to have
the highest mass transfer rate coefficient. However, the calculation of
Henry's Law constant (see Table 3.4) indicates that the highest ammonia
solubility is expected to occur in the solution with the lowest S04~ con-
centration when NaOH was used for pH adjustment.
The mass transfer rate coefficients for solutions A and B were
approximately the same when pH was adjusted using Ca(0H)2. The relatively low
K values found in these two cases indicates that addition of NaOH may have a
slight advantage.
No correlation between ionic strength and mass transfer rate coefficient
can be found.
3.4 SUMMARY
Analyses of the estimated Henry's Law constant and changes in
solubilities of ammonia (as given in Table 3.4, page 14) indicate that
addition of a caustic, compared with slaked lime, can result in higher Henry's
Law constant and lower ammonia solubilities for the three waste streams
considered. These effects can be attributed to the relatively high ionic
strength that occurred in wastewaters when pH was adjusted with NaOH. Between
solutions B and C, where the sulfate concentration was varied without changing
the solution strength (total number of moles), no significant difference in
Henry's Law constant or solubility could be seen for either of the two pH
adjustment methods. The highest Henry's Law constant and corresponding lowest
ammonia solubility were observed in solution A, which has the highest molal
strength.
Experimental studies to determine the effects of dissolved species and pH
adjustment method on the mass transfer rate coefficient (K) indicate that
those effects are relatively low and the maximum changes in mass transfer rate
30
-------
TABLE 3.11. MASS TRANSFER RATE COEFFICIENTS FOR AWONIA
IN DIFFERENT WASTE STREAMS
pH Adjustment with NaQH pH Adjustment with Ca(QH)?
Solution
Ionic Strength®
(g ion/L)
Kb
(min-1)
Ionic Strength*
(g ion/L)
Kb
(min-1)
A
1.546
0.0165
1.034
0.0132
B
1.111
0.0199
0.840
0.0138
C
1.343
0.0158
0.706
0.0170
a Ionic strength is the summation of I values given in Table 3.4 for a
given solution.
b K is mass transfer rate coefficient.
31
-------
coefficient do not exceed 25 percent. In two of the three different
solutions, however, the mass transfer rate coefficients were higher for the
waste stream where pH was adjusted using caustic. For solutions with
approximately the same S04- concentration but different molal strength, the
mass transfer rate coefficients were comparable when NaOH was used as the pH
adjustment method. For Ca(0H)2, however, the K values were comparable where
both the molal strength and S04~ level were different. The overall analysis
of data indicate that, when compared with lime, addition of NaOH can promote
ammonia removal for solutions with relatively low S04~ levels (5,000 mg/L).
32
-------
4. TASK 2: AMMONIA REMOVAL STUDIES USING
STEAM STRIPPING UNIT
4.1 OBJECTIVE AND SCOPE
The purpose of this task was to study the removal of ammonia from synthet
wastewaters using a steam stripping apparatus. A laboratory scale steam
stripping unit was designed and constructed. Experiments were conducted us-
two different synthetic waste streams. The pH of each waste stream was
adjusted using NaOH or CaO. Ammonia removal was studied under different pH
adjustment methods and different steam to wastewater ratios.
4.2 DESIGN AND CONSTRUCTION OF THE STEAM STRIPPING UNIT
Steam stripping is used to process wastewater containing high concentra-
tions of ammonia, e.g., from steel, petrochemical, fertilizer, organic
chemical, and nonferrous metal-manufacturing operations. The cost of steam
production is partly offset by the recovery and reuse of ammonia.
Efficiency of ammonia removal by steam stripping is governed by the
following factors (Patterson, 1985):
1. Proper design of the stripper
2. Control of hydraulic flowrates
3. Adequate steam
4. pH levels of 11 or above
5. Temperatures of 200°F or above in the stripper
6. Sufficient droplet detainment space.
These factors were taken into consideration during the design of the steam
stripping unit.
4.2.1 Characteristics of the Column
4.2.1.1 Flow
Gas transfer can be effected by various devices including tray columns,
cross-flow packed columns, and counter current packed columns. Counter
33
-------
current packed columns are generally used for removing ammonia, hydrogen
sulfide, and carbon dioxide because of the continuous and thorough contact of
the liquid with the gas. Counter current flow also minimizes the thickness of
the water layer on the packing, thus enhancing mass transfer. A counter
current column was chosen for this study.
4.2.1.2 Column Packing-
Packing is available in different shapes (e.g., saddles, Pall rings,
tellerettes), materials (e.g., ceramic, steel, plastic), and sizes (e.g., 1/2
in., 1 in., 2 in.). Packing material suitability is determined by evaluating
its operating characteristics and cost. For this high temperature and high pH
application, certain plastic materials like Teflon and Kynar (PVDF) were found
suitable. Kynar appears to be more cost effective. Kynar has a maximum
operating temperature of 302°F and a heat distortion temperature of 250 F. It
is also compatible with a large number of chemicals. Hence, Kynar was
selected as the packing material.
Packing material shape and size are characterized by packing factor (ft"1)
and surface area (ft2/ft3 of column). Larger packings are less expensive on a
unit volume basis and allow higher wastewater loading rates. Smaller packings
provide larger mass transfer rate coefficients and hence smaller column
heights. Therefore, for a high degree of removal, smaller packings can be
more economical. It is recommended that the column diameter should be at
least 8 to 10 times the nominal size of the packing in order to avoid poor
liquid distribution due to wall effects. For a column of 7 in. diameter,
5/8-in. Pall rings (which have a packing factor of 97 ft"1 and a surface area
of 104 ft2/ft3) can be used. This size of Pall ring has a smaller surface
area than 1/2-in. Berl saddles (surface area = 142 ft2/ft3), but a greater
capacity (packing factor for 1/2 in. Berl saddles is 140 ft"1).
4.2.1.3 Column Material--
The column material should be able to stand high temperatures and pH
conditions. Kynar, Teflon, crystal glass, and stainless steel are some of the
materials that can be used for stripping column. Glass was chosen as the
column material because (a) it is economical and (b) the flow characteristics
and scaling can be observed from outside.
34
-------
4.2.2 Design of the Stripping Unit
The design of the counter current packed bed column involved the following
steps:
]. Determination of the Henry's Law constant for NH3 at the temperature
of the column (100'C)
2. Determination of the steam-wastewater ratio and the NTU (number of
transfer units)
3. Calculation of the steam mass flowrate (lb/ft2-hr) and a suitable
column diameter
4. Calculation of the HTU (height of a transfer unit), and hence the
height of the packing.
The column was designed for a temperature of 100 'C. The wastewater was
adjusted to a pH of 11 or more. Raising the pH to 11 transforms most of the
NH4+ to NH3.
4.2.2.1 Henry's Law Constant-
Henry's constants are strongly influenced by temperature. Most available
data lists the Henry's constant (H) for ammonia to be 0.76 atmL/moles at
20°C. If the enthalpy change caused by dissolution of a contaminant in water
is considered independent of temperature, the relation
- H°
log H - M + K (12)
RT
can be used to determine H at 100*C (Kavanaugh and Trussell, 1980). Here
R = universal gas constant = 1.987 kcal/kmol-®K; T = temperature (*K);
H° = change in enthalpy due to dissolution; and K = constant. For ammonia,
H3 = 3.754 x 103 kcal/kmol and K - 6.31. At 100 C (373"K) for ammonia, H is
calculated to be 17.6 atm.
4.2.2.2 Number of Transfer Units--
The height of the column packing, Z = (HTU)x(NTU), where HTU is the height
of a transfer unit and NTU is the number of transfer units. NTU is equivalent
35
-------
to the number of theoretical trays required to bring about a certain degree of
removal. NTU also depends on the stripping factor, R, which is given by the
following equation:
R = H(G/L) (13)
Here, G = mass velocity of steam (moles/ftz-sec), and L = mass velocity of
wastewater (moles/ftz-sec). The dependence of NTU on removal efficiency and
stripping factor is plotted by Treybal (1980). This graph (Figure 4.1) shows
very little increase in efficiency for R > 5. For 99.9 percent removal at R =
5, the NTU - 8. These values of R and NTU were taken in the design.
The steam-wastewater ratio can then be calculated from R - 5 and H -
17.6 atmL/moles. Hence, G/L - 0.284 x (molar ratio)
mol. wt. NH,
- °'284 * mol. wt. HgO * °'284 * I17"8'
= 0.27 (mass ratio)
4.2.2.3 Diameter of the Column--
In a packed column, for a given liquid loading rate, gas pressure drop
increases approximately as the square of the gas velocity. At very high gas
flowrates, flooding may occur. This can be characterized by a rapid increase
in gas pressure drops. Packed columns are usually designed to operate well
below flooding conditions (about 40 to 50 percent). A generalized pressure
drop correlation for a packed column is shown by McCabe and Smith (1984) in
(Figure 4.2). Here the abscissa is
(L/G) xfdg/dj0'5
and the ordinate is G^ F (62.3/d.)
p L L (14)
9C dL dg
where Fp = packing factor, ft"1
dL = density of wastewater, lb/ft3
dg = density of steam, lb/ft3
36
-------
II) 1 1 j
T
1
¦ ¦!
L1 ,,:p.6hd
6
i
fcb
»* V
0 996
0 997
0 998
0 9990
0 9972
0 99-U
3 4 5 6 B 10 20
MufflC* 0' Utitl [NTU)
30 JO 50
Figure 4.1. Dependence of NTU on removal efficiency and
stripping factor.
(Source: Montgomery, 1985)
37
-------
Paromattr ofarvts a irtssurt
tirop m inchti of meter/foot
of peeked ttnghr
0.060
0020
0.010
s
as
0.4 0* 10
O.Ot 0.02 0 04 0060.1
*06000
Figure 4.2. Generalized correlation for flooding and
pressure drop in packed columns'.
(Source: McCabe and Smith, 1984)
38
-------
"L = viscosity of wastewater, cP
g » Newton's-Law proportionality factor, 32.174 ft-lb/lbf-s2
2
L = mass velocity of wastewater, lb/ft -hr
2
6 = mass velocity of steam, lb/ft -hr.
For 5/8" Pall rings, Fp = 97. The densities of wastewater (assumed as water)
and steam for the column temperature (100'C) are dL - 59.8 lb/ft3 and
dg = 0.03731 lb/ft3. The viscosity of water at 100*C is « 0.284 cP.
The abscissa is, therefore, g g
(L/G)x(dg/dL) 0,5 = (1/0.27)x(0.03731/59.8) ' = 0.09
From the graph, the ordinate for flooding is 0.14.
G2F (62.3/d ) n°-Z
_£ L L = 0.14
9c dL dg
G2 (97) (62.3/59.8) (0.284) °*2
= 0.14
(32.174) (59.8) (0.03731)
Thus, G at flooding = 0.358 lb/ft2-s
= 1288 1b/ft2-hr
If the column is operated at 50 percent of flooding, then the designed steam
2
capacity becomes G - (0.5) (1288) -= 644 lb/ft -hr. At this design capacity,
the mass velocity of the liquid would be
L = 644/0.27 = 2385 lb/ft2-hr.
If a wastewater flowrate of 600 lb/hr is desired, the required cross-
2
sectional area of the column is 600/2385 = 0.252 ft . This corresponds to a
diameter of 6.8 inches. For this study a column diameter of 7 inches was
chosen. Thus, the designed capacity of this 7-inch diameter column is as
follows:
Wastewater flowrate = 600 lb/hr
= 1.2 gallons per min (gpm)
Steam flowrate = 644 x (area of column)
39
-------
= 644 x 0.252
= 162 lb/hr
= 72 ft3/min (cfm)
Steam wastewater ratio = 2.25 lb steam/gallon of wastewater.
4.2.2.4 Height Equivalent to a Transfer Unit--
Often, the values of individual mass transfer rate coefficients vary
rapidly with flowrates. Hence, the quantity obtained by dividing each mass
transfer rate coefficient by the flowrate is more nearly constant than the
coefficient itself (Perry, 1973). This new quantity is called the height of
one transfer unit (HTU). From Perry (1973),
HTU = (l/a)x(L//iL)nx[/iL/ (d^)]05 (14)
For 5/8-inch Pall rings, a and n are approximately 150 and 0.28 respectively.
Here fi^ is given in lb/ft-hr. Thus, = 0.284 cP, = 0.687 lb/ft-hr.
Dl is the diffusion coefficient of NH^ in the wastewater expressed in
ft2/hr. For the NH^-HjO system at 25'C, D » 2.0 x 10 cm2/s. The value at
100'C is calculated by using the relationship D /j/T = constant. Thus, D at
100°C is 7.651 x 10 cm2/s or 2.965 x 10"4 ft2/hrl" L
Using this value of D , HTU « 0.39 ft. This gives a packing depth, Z =
(NTU) x (HTU) = 8x0.39 - 3.12 ft. Thus, the designed column is 7 inches in
diameter and has a 3 foot packing depth.
The column is made of glass to facilitate observing the flow charac-
teristics and solid deposition/scaling in the column. Mechanical strength is
provided by four external steel bars. Liquid distribution is by means of a 4-
armed liquid stream device. About 6 inches of space is provided above and
below the packing. Two thermocouples are installed to monitor temperatures
near the top and bottom of the packing. A heat exchanger is provided to pre-
heat the wastewater before entering the column.
4.2.3 Scale-Up
Columns with larger diameters will be required for increased wastewater
flowrates. If the same packing is used, the variation of column diameter with
loading rate is given in Table 4.1. The calculation procedure given in the
40
-------
previous section was used and the stripping factor (R) was assumed to be the
same. The 5-fold increase in wastewater flowrate (1.2 to 6 gpm) resulted in
an approximately 2-fold diameter increase.
Larger sized packing may be used for higher capacity, i.e. smaller
diameters for a given flowrate as seen 1n Table 4.2 and Figure 4.3. The ratio
of diameter of column to size of parking should be maintained at 10. Higher
capacity is slightly offset however, by the increase in height of packing.
For larger columns, a 1-inch packing may be the most efficient.
Table 4.3 and Figure 4.4 show the effect of different stripping factors on
column size. With increasing R, the diameter increases. The height of the
column however decreases.
Even though the general procedure is the same for design of commercial -
scale columns, pilot studies are often necessary for establishing scale-up
factors and estimating costs.
4.3 EXPERIMENTAL PROCEDURES
This section describes the methods used to operate the bench scale steam
stripping unit used in Task II of this study. The design and construction of
the steam stripping column is discussed in Section 4.2. The system was
designed to pump a high pH synthetic wastewater influent to the top of the
packing material in the column casing. As shown in Figure 4.5, the wastewater
flows down over the packing material and exits through the effluent line at
the column base. Steam is injected into the column at the base of the packing
material. As the wastewater passes through the jet of steam, it is heated to
100°C. Flowrates for the steam and/or the influent wastewater are varied to
determine the variation of ammonia removal efficiency. Wastewater was pumped
to the stripping unit using 1/8 hp MAC* variable flowrate pump. The flowrate
for the influent was adjusted using valves and monitored using a Brooks* flow
meter. The steam flowrate was measured by condensing steam entering the column
and measuring changes in the flowrate of column effluent. The steam flow
entering the column was controlled using a valve/orifice unit (Figure 4.5) and
monitored using two pressure gauges located on either side of the orifice.
The column hood vent was sealed to prevent steam from escaping the column.
Iced tap water was used as influent to ensure complete condensation of the
41
-------
TABLE 4.1. COLUMN DIAMETER FOR 1/2-INCH PACKING AND R=5
Wastewater Flcyrate " Column Diameter
(.gpm } {lb/hr ) ( inches)
1.2
600
7
3
1500
11
4
2000
12
6
3000
15
10
5000
20
20
10000
28
42
-------
TABLE 4.2. EFFECT OF PACKING SIZE
Wastewater Flowrate
Diameter of Column
(in.)
Heioht of Column
(ft)
(lb/hr)
Packing Size
Packing Size
5/8
in. 1 in.
2 in.
5/8
in. 1 in.
2 in.
600
7
-
-
3.0
-
-
1500
11
-
-
3.0
3.0
3.58
2000
12
11
-
3.0
3.0
3.58
3000
15
13
-
3.0
3.0
3.58
5000
20
17
-
3.0
3.0
3.58
10000
28
24
21
3.0
3.0
3.58
43
-------
30
-a. Pall rings
a Pall rings
o Pall rings
5/8 in.
1 in.
2 in.
D 2000 4000 6000
Wastewater flowrate, lb/hr
8000
10000
12000
Figure 4.3. Flowrates and packing size.
-------
TABLE 4.3. DIMENSIONS OF THE COLUMN FOR VARIOUS VALUES
OF R FOR 5/8-INCH PACKING
Wastewater Flowrate Diameter of Column (in.) Height of column (ft)
(Ib/hr) Stripping Factor Stripping Factor
R=1 R=3 R=5 R=1 R=3 R=5
600
6
7
7
4.3
, 3.58
3.0
1500
7
9
11
4.3
3.58
3.0
2000
8
11
12
4.3
3.58
3.0
3000
9
13
15
4.3
3.58
3.0
5000
12
17
20
4.3
3.58
3.0
10000
17
24
28
4.3
3.58
3.0
45
-------
Heights are for 5/8 in. rings
"1 1 1 1 : 1 1
0 1 2 3 4 5 6
Stripping factor (R)
Figure 4.4. Stripping factors and height of column.
-------
steam. The effluent flowrate was verified by direct measurement of flow
volume per unit time prior to turning on the steam. Three different pressure
settings were used to supply steam to the column. The column effluent
flowrate was compared to the steam pressure. The calibration curve was
derived by plotting changes in effluent flow against the corresponding
pressure gauge settings (see Figure 4.6).
A total of nine steam stripping experiments were performed to compare two
synthetic wastewater compositions and to compare the use of NaOH or CaO (lime)
for pH adjustment of the solutions. The two wastewater compositions used for
this study are as follows:
Concentration in Concentration in
Chemical Species Wastewater B (ma/1) Wastewater C (ma/1)
NH3-N 5,000 5,000
Mg~ ZOO 200
Na* 11,939 11,939
S04= 5,000 20,000
CI" 28,000 16,905
Solutions were prepared in 50- or 100-gallon batches, and actual species
concentrations were verified by analysis.
In each experiment the influent was prepared from Baker Analyzed Reagents
and dissolved in tap water. Then the pH was adjusted to approximately 12 with
either 10N NaOH or bulk dry CaO and the solution was mixed gently. Wastewater
was pumped to the stripping column by a variable flowrate pump that could be
adjusted to set a desired flowrate. Steam was turned on and the pressure
gauges were adjusted to steam flowrate at the desired flow. When the column
conditions had equilibrated, as indicated by the effluent and column
temperatures, effluent samples were taken at regular time intervals and
measured for ammonia concentration. Samples were also taken from the influent
for initial ammonia concentration, pH, and other dissolved species both before
and after pH adjustment. Wastewater influent and effluent temperatures and
steam temperature were also recorded.
47
-------
¦U
CO
Mixing
Device
©
Filter
«*»
Synthetic
Wastewater
100 gal. Wastewater
Tank
Flowmeter
lq-
Water
Pump
Heated
Wastewater
Exchanger
I
Steam out
Turn
Steam
Snipping
Column
Ut
—©
Packing Materials
Mi)
Steam In
Wastewater
out
Orifice
a.
Q.
U)
M
C
a
S
T •> Thermocouple
P " Pressure Gauge
V b Valve
Figure 4.5. Experimental set up for ammonia removal by steam stripping.
-------
tO
£
.o
01
4-»
f0
$-
2
o
E
-------
4.4 RESULTS AND DISCUSSION
The experimental results of the steam stripping of ammonia are given in
Tables 4.4 through 4.12. Since the maximum steam flowrate attainable from the
system was 1 lb/min, the wastewater flowrate was maintained at or below
2 L/min (0.53 gal/min). The preliminary studies with solution B and pH
adjustment with NaOH (A-NaOH system) indicated that if the steam to wastewater
ratio is 1.3 lb/gal, the removal of ammonia from a stream with 5,200 ppm of
NH3-N was as low as 93 percent. Increased steam-wastewater ratios resulted in
higher removals (Tables 4.4 and 4.5).
Addition of CaO to solution A resulted in 12"C increase in temperature due
to the exothermic nature of CaO dissolution (Tables 4.6 and 4.7). Even with
the increased influent temperatures, the ammonia removal efficiency was over
3 percent less for B-CaO system when compared to that of B-NaOH system.
Results given in Table 3.4 on Henry's Law constant and the mass transfer rate
coefficient for B-NaOH (0.0199 min"1) is higher than that for the B-Ca(OH)2
system (0.0138 min"1). The solubility of NH3 in the B-NaOH system is lower
than that for the B-Ca(0H)e system (Table 3.4). These data indicate that pH
adjustment with caustic can improve the ammonia removal slightly over the lime
in waste streams with relatively low S04" levels (5,000 mg/L).
The experiments conducted with solution C showed that the ammonia removal
was slightly higher for those where pH was adjusted with CaO than those where
it was adjusted with NaOH (Tables 4.8, 4.9, 4.11, and 4.12). However, these
differences were smaller than those observed for solution B. It is important
to note that the differences in mass transfer rate coefficient followed a
similar trend (Table 3.11). The K value for the C-Ca(0H)2 system was slightly
higher than that for the C-NaOH system. In contrast, the Henry's Law constant
was slightly higher for the C-NaOH system (8.3 x 10~4) when compared to the
C-Ca(0H)2 system.
Comparison of data in Tables 4.8 and 4.10 indicate that wastewater
preheating can also improve the ammonia removal efficiency. The increase in
influent wastewater temperature by 19°C resulted in a 2 percentile increase in
the ammonia removal efficiency. More than 99.9 percent removal can be
achieved by increasing the steam-wastewater ratios up to 3.8 lb/gal.
50
-------
TABLE 4.4. RESULTS FOR PILOT RUN NO. P-l FOR
WASTEWATER B and NaOH
Wastewater Characteristics
Concentration,
mq/L
Species
Before pH adjustment
After pH adjustment
NH4
5,600
5,200
SO4
11,200
10,900
cr
35,200
32,500
Mg**
201
<10
Na+
16,000
26,000
Ca+*
40
<10
Test Conditions
wastewater flow rate = 2 L/min
steam flow rate = 1 lb/min
steam temperature = 114°C
wastewater influent temperature = 26°C
wastewater effluent temperature = 101°C
wastewater influent pH = 12.5
base used to adjust pH = NaOH
Test Results of Column
Effluent Analysis
Effluent
NH3-N
T ime
Concentration
(min)
(mq/L)
Percent Removal
5
79
98.5
10
32
99.4
15
7.8
99.B
20
7.4
99.9
25
102
98.0
average percent removal of ammonia = 99.1
steam to wastewater flow rate ratio = 1.9 lb steam/1 gallon wastewater
51
-------
TABLE 4.5. RESULTS FOR PILOT RUN NO. P-2 FOR
WASTEWATER B and NaOH
Wastewater Characteristics
Concentration,
mq/L
Species
Before pH adjustment
After pH adjustment
NH4
5,600
5,200
SO4
11,200
10,900
CI"
35,200
32,500
Mg44
201
<10
Na+
16,000
26,000
Ca++
40
<10
Test Conditions
wastewater flow rate = 2 L/min
steam flow rate = 0.7 lb/min
steam temperature = 114°C
wastewater influent temperature = 26°C
wastewater effluent temperature = 101°C
wastewater influent pH = 12.5
base used to adjust pH = NaOH
Test Results of Column Effluent Analysis
Time
(min)
Effluent
NH3-N
Concentration
(mq/L)
Percent Removal
5
255
95.1
10
330
93.7
15
380
92.7
20
420
91.9
25
400
92.3
average percent removal of ammonia = 93.1
steam to wastewater flow rate ratio = 1.3 lb steam/1 gallon wastewater
52
-------
TABLE 4.6. RESULTS FOR PILOT RUN NO. P-3 FOR
WASTEWATER B and CaO
Wastewater Characteristics
Concentration, mq/L
Species
Before pH adjustment
After pH adjustment
NH4
6,600
5,100
sol
6,300
2,100
CI"
38,500
32,500
Mg++
271
<10
Na+
20,000
15,000
Ca++
30
6,000
Test Conditions
wastewater flow rate = 2 L/min
steam flow rate = 1 lbs/min
steam temperature = 115°C
wastewater influent temperature = 38°C
wastewater effluent temperature = 101°C
wastewater influent pH = 11.72
base used to adjust pH = CaO
Test Results of Column Effluent Analysis
Effluent
NH3-N
Time Concentration
(min) (mq/L) Percent Removal
17 288 94.3
22 270 94.7
27 260 94.9
32 200 96.1
37 188 96.3
average percent removal of ammonia * 95.26
steam to wastewater flow rate ratio * 1.9 lb steam/1 gallon wastewater
53
-------
TABLE 4.7. RESULTS FOR PILOT RUN HO. P-4 FOR
WASTEWATER B and CaO
Wastewater Characteristics
Concentration, tnq/L
Species
NH4
SO4
cr
Mg44
Na+
Ca++
Before pH adjustment
6,600
6,300
38,500
271
20,000
30
After pH adjustment
5,000
2,100
32,500
<10
15,000
6,000
Test Conditions
wastewater flow rate
steam flow rate
steam temperature
wastewater influent temperature
wastewater effluent temperature
wastewater influent pH
base used to adjust pH
1 L/min
1 lbs/min
115°C
39°C
101°C
11.72
CaO
Test Results of Column
Effluent Analysis
Effluent
NH3-N
Time
Concentration
(min)
(mq/L)
Percent Removal
2
16
99.7
5
13
99.7
8
13
99.7
11
13
99.7
14
12
99.8
average percent removal of ammonia * 99.7
steam to wastewater flow rate ratio = 3.8 lb steam/1 gallon wastewater
54
-------
TABLE 4.8. RESULTS FOR PILOT RUN NO. P-5 FOR
WASTEWATER C and NaOH
Wastewater Characteristics
Concentration.
ma/L
Species
Before pH adjustment
After pH adjustment
NH4
4,850
4,750
SO4
39,000
41,000
cr
20,500
21,500
Mg++
223
<10
Na+
14,300
30,000
Ca++
40
30
Test Conditions
wastewater flow rate « 2 L/min
steam flow rate ¦ 1 lbs/min
steam temperature ® 115°C
wastewater influent temperature = 26°C
wastewater effluent temperature = 101°C
wastewater influent pH = 11.67
base used to adjust pH * NaOH
Test Results of Column
Effluent Analysis
Effluent
NH3-N
Time
Concentration
(min)
(mq/L)
Percent Removal
5
198
95.8
10
175
96.3
15
121
97.4
20
125
97.4
25
126
97.4
average percent removal of ammonia = 96.9
steam to wastewater flow rate ratio = 1.9 lb steam/1 gallon wastewater
55
-------
TABLE 4.9. RESULTS FOR PILOT RUN NO. P-6 FOR
WASTEWATER C and NaOH
Wastewater Characteristics
Concentration,
mq/L
Species
Before pH adjustment
After pH adjustment
NH4
4,850
4,700
SO4
39,000
41,000
CI"
20,500
21,500
Mg++
223
<10
Na+
14,300
30,000
Ca++
40
30
Test Conditions
wastewater flow rate =
steam flow rate -
steam temperature =
wastewater influent temperature =
wastewater effluent temperature »
wastewater influent pH =
base used to adjust pH =
1 L/min
1 lbs/rain
115°C
26°C
101°C
11.67
NaOH
Test Results of Column
Effluent Analysis
Time
(min)
Effluent
NH3-N
Concentration
(mg/L)
Percent Removal
5
4.4
99.91
10
4.5
99.90
15
4.2
99.91
20
4.2
99.91
25
3.9
99.92
average percent removal of ammonia =
steam to wastewater flow rate ratio =
99.9
3.8 lb steam/1 gallon wastewater
56
-------
TABLE 4.10. RESULTS FOR PILOT RUN NO. P-7 FOR
WASTEWATER C and NaOH
Wastewater Characteristics
Concentration,
mq/L
Species
Before pH adjustment
After pH adjustment
NH4
3,950
SO4
30,000
8,800
cr
18,500
18,500
Hg-n-
186
<10
Na+
11,800
14,000
Ca++
30
1,700
Test Conditions
wastewater flow rate
steam flow rate
steam temperature
wastewater influent temperature
wastewater effluent temperature
wastewater influent pH
base used to adjust pH
2 L/min
1 lbs/min
115°C
47°C
101°C
11.91
CaO
Test Results of Column Effluent Analysis
Time
(""")
5
10
15
20
25
Effluent
NH3-N
Concentration
C«nq/L)
79
80
80
2
2
Percent Removal
98.0
98.0
98.0
99.95 *
99.95
average percent removal of ammonia = 98.8
steam to wastewater flow rate ratio = 1.9 lb steam/1 gallon wastewater
57
-------
TABLE 4.11. RESULTS FOR PILOT RUN NO. P-8 FOR
WASTEWATER C and CaO
Wastewater Characteristics
Concentration, mq/L
Species Before pH adjustment After pH adjustment
NH4
3,950
SO4
30,000
8,800
CI"
18,500
18,500
Mg++
186
<10
Na+
11,800
14,000
Ca++
30
1,700
Test Conditions
wastewater flow rate = 2 L/min
steam flow rate = 1 lbs/min
steam temperature = 115°C
wastewater influent temperature = 39°C
wastewater effluent temperature = 101°C
wastewater influent pH = -11.91
base used to adjust pH = CaO
Test Results of Column
Effluent Analysis
Effluent
NH3-N
Time
Concentration
(min)
(mq/L)
Percent Removal
5
87
97.8
10
91
97:7
15
90
97.7
20
92
97.7
25
92
97.7
average percent removal of ammonia = 97.7
steam to wastewater flow rate ratio = 1.9 lb steam/1 gallon wastewater
58
-------
TABLE 4.12. RESULTS FOR PILOT RUN NO. P-9 FOR
WASTEWATER C and CaO
Wastewater Characteristics
Concentration, roq/L
Species Before pH adjustment After pH adjustment
NH4 3,825
SO4 30,000 8,800
CI' 18,500 18,500
Mg++ 186 <10
Na+ 11,800 14,000
Ca++ 30 1,700
Test Conditions
wastewater flow rate
steam flow rate
steam temperature
wastewater influent temperature
wastewater effluent temperature
wastewater influent pH
base used to adjust pH
1 L/min
1 lbs/min
115°C
39°C
101°C
11.91
CaO
Test Results of Column Effluent Analysis
Time
(min)
5
10
15
20
25
Effluent
NH3-N
Concentration
(m/l)
2.2
1.5
1.3
1.3
1.1
Percent Removal
99.94
99.96
99.97
99.97
99.97
average percent removal of ammonia = 99.96
steam to wastewater flow rate ratio = 3.8 lb steam/1 gallon wastewater
59
-------
4.5 SUMMARY AND CONCLUSIONS
The results of the steam stripping study are summarized in Table 4.13.
Data show that when the steam-wastewater ratios are low (1.3 lb/gal), the
ammonia removal efficiency was as low as 93 percent. By increasing steam-
wastewater ratios to 3.8 lb/gal, removals of oyer 99.9 percent have been
observed. The removal efficiency in one test study was improved by
2 percentile points when the temperature of the influent waste stream was
raised by about 20"C. One of the advantages of using lime is its ability to
raise the wastewater temperature during pH adjustment because hydration of
lime is an exothermic process.
For wastewater with low initial S04" level (5,000 mg/L), ammonia removal
was 3 percent higher when pH was adjusted with caustic rather than lime.
These observations are in agreement with the trends predicted from the
estimated Henry's Law constant and mass transfer rate coefficient. In the
experiments conducted with wastewaters using higher initial SO^ levels
(20,000 mg/L), ammonia removal was slightly higher when pH was adjusted with
lime instead of caustic. These observations are in agreement with the
conclusions reached from the corresponding mass transfer rate studies that did
not agree with the theoretical estimates of solubilities based on the Henry's
Law constant.
In summary, over 99.9 percent removal of ammonia can be achieved by
introducing a high steam-wastewater ratio such as 3.8 1b/gal1 x»nJ Variation of
chemical constituent such as S04= and the molal strength have only a little
effect on net NH3 removal. Higher removal efficiencies can be achieved by
preheating wastewaters and operating the stripping tower at high temperatures
by increasing the steam-wastewater ratios.
60
-------
TABLE 4.13. SUMMARY RESULTS OF LABORATORY STUDY ON STEAM STRIPPING
Wastewater Temp. °C
pH Steam to mm ^ ^ *¦
Adjustment Column Column Wastewater Ratio — Average NH3
Wastewater Method Influent Effluent lb/gallon Influent Effluent Removal, %
B (low SO4)
C (high SO4)
NaOH
26
101
1.9
5,200
32-102
99.1
NaOH
26
101
1.3
5,200
255-420
93.1
CaO
38
101
1.9
5,100
188-288
95.3
CaO
39
101
3.8
5,000
12-16
99.7
NaOH
26
101
1.9
4,750
121-198
96.9
NaOH
26
101
3.8
4,700
3.9-4.5
99.91
NaOH
47
101
1.9
3,950
2.0-80
98.8
CaO
39
101
1.9
3,950
87-92
97.7
CaO
39
101
3.8
3,825
1.1-2.2
99.96
-------
5. ENGINEERING COST ESTIMATES
5.1 OBJECTIVE AND SCOPE
The physical and chemical characteristics of waste streams, from 9
nonferrous metals processing plants, containing high levels of ammonia are
given in Table 5.1. The waste characteristics varied significantly from one
plant to the other; establishing one stream with "typical characteristics for
high-strength ammonia wastewater" was not seem practical. Consequently four
waste streams were selected to represent the whole range of ammonia
wastewaters. These are Plants 1, 2, 3, and 5. The distribution of chemical -
species after addition of the base was estimated by employing the geochemical
equilibrium and reaction path models EQ3/EQ6 (Wolery, 1979, 1983, 1987). The
wastewater characteristics used for the input of EQ3/EQ6 are listed in
Table 5.2. Data on the quantity of alkali, either lime or sodium hydroxide,
needed to raise the pH of metal winning wastewaters to 11.5 was generated.
High pH favors the formation of ammonia, NH3, which can be stripped from
aqueous solutions. The program showed that alkali addition would produce
precipitate which must be removed before stripping.
In this task the costs of a number of common wastewater treatment unit
processes were investigated. Estimates of the costs for chemical addition,
sludge removal, and thickening were made using the wastewater characteristics
of Plants ], 2, 3, and 5. Included in these estimates were costs for mixing
facilities, chemicals, and sludge removal, concentrations, handling, and
transport. Not included were costs for chemical storage facilities or
buildings, land, or costs for disposal of sludge--all of which are likely to
vary considerably from site to site. These cost values were generated for a
variety of wastewater flowrates.
62
-------
TABLE 5.1. CHEMICAL ANO PHYSICAL CHARACTERISTICS OF METAL PROCESSING WASTEWATERS CONTAINING AffWNlAi CONCENTRATION IN ag/L8
Chenlcal
Species
Plant 1
Plant 2
Plant 3
Plant 4
Plant 5
Plant 6
Plant J
Plant 6
Plant 9
NHj
1,000-6,000
5,300-11,000
2,300
4,300
6,500-13,000
13,000-16,000
2,800
3400
22,000
Ca
18,000
21
9,600
_b
10-15
500
NRC
NR
NR
CI
1,300
>19,000
45,000
-
3,700-19,000
66, (MO
NR
16,000
150
F
55,000
2.2
-
5,600
2
-
-
42
30,000
Hg
1,300
395
21
-
150-180
NR
NR
NR
«a
810
21,000
16,000
56
13,000-20,000
NR
NR
NR
NR
so4
21,000
34,000
1,000-2,500
130
400-4,800
-
NR
170
-
«3
NR
NR
NR
NR
NR
NR
NR
NR
36,000
Sb
<0.003
0.14
NR
NR
NR
NR
NR
NR
NR
AS
0.47
0.0037
NR
NR
NR
NR
NR
NR
NR
Be
550
<0.02
NR
NR
NR
NR
NR
NR
NR
Cd
0.23
<0.03
NR
NR
NR
NR
NR
NR
NR
Cr
1)
<0.10
NR
NR
NR
NR
NR
NR
NR
Cu
13
0.56
NR '
NR
NR
NR
NR
NR
NR
CN*
21
0.036
NR
NR
NR
NR
NR
NR
NR
-------
TABLE 5.1. (continued)
ChemJcil
Species
Plant 1
Plant 2
Plant 3
Plant 4
Plant 5
Plant 6
Plant 7
Plant 8
Plant 9
Pb
2.3
18.0
NR
NR
NR
NR
NR
NR
NR
Hg
<0.0002
0.0091
NR
NR
NR
NR
NR
NR
NR
HI
3.9
1.2
NR
NR
NR
NR
NR
NR
NR
Se
<9.003
0.08
NR
NR
NR
NR
NR
NR
NR
Te
<0.002
0.0B1
HR
NR
NR
NR
NR
NR
NR
Zn
4.1
<®.l
NR
NR
NR
NR
NR
HR
NR
A1
69
2.4
NR
NR
NR
NR
NR
NR
NR
Ba
3.3
0.15
NR
MR
NR
NR
NR
HR
HR
B
29
27
NR
NR
NR
NR
NR
NR
NR
Co
0.23
18
NR
NR
NR
NR
NR
NR
HR
Fe
630
2.3
NR
NR
NR
NR
NR
NR
NR
Mn
8.1
0.21
NR
NR
NR
NR
NR
NR
NR
Ho
0.53
44
NR
NR
NR
NR
NR
NR
NR
TS
150,000
170,000
93,000
4,200
47,000-150,000 110,000-120,000
NR
46,000
NR
IDS
20,000
140,000
NR .
3, BOO
38,000-140,000
-
NR
44,600
15,000
-------
TABLE 5.1. (continued)
Chemical
Species
Plant 1
Plant 2
Plant 3
Plant 4
Plant S
Plant 6
Plant 7
Plant B
Plant 9
TSS
130,000
230
2,300
34
180-280
300-400
40-60
82
110
PHd
9.2B-11.2
3.0
10.
8.0
1.0-2.0
B.4-S.8
0.B-1.2
NR
9.75
• All the values are In ng/L except pH.
t> Negligible.
c NR, not reported,
d Standard pH units.
-------
TABLE 5.2. CHARACTERISTICS OF REPRESENTATIVE WASTEWATER STREAMS.
Chemical
Species
Concentration
. mq/L
Plant 1
Plant 2
Plant 3
Plant 5
Cr
13
-
-
-
Cu
13
-
-
-
Pb
2.3
18
-
-
Ni
3.9
1.2
-
-
Zn
4.1
-
-
-
AT
6.9
2.4
-
-
nh3
5,000
10,000
2,300
12,000
Ba
3.3
-
-
-
B
29
27
-
-
Ca
20
21
50
15
CI
1,300
20,000
45,000
18,000
Co
-
18
-
-
F
55,000
2.2
-
2
Fe
630
2.3
-
-
Mg
1,300
395
21
180
Mn
8.1
-
-
-
Na
810
21,000
16,000
18,000
SO4
21,000
34,000
2,500
4,800
PH4
4.5
4.5
4.5
4.5
a pH is in standard units.
66
-------
5.2 METHODS
5.2.1 Eouilibria Model 1ino
The data given in Table 5.2 are the wastewater characteristics that were
entered into the computer program EQ3/EQ6. The program simulates equilibrium
conditions 1n single or multicomponent solutions, calculating the distribution
of the chemical species once equilibrium has been established. This
distribution will include the species concentration in solution as well as the
quantity of chemical species that may have been precipitated. The program's
internal data base contains information on the hydrolysis constants and
solubility products of many of the chemical species that appear in
high-strength ammonia wastewaters. Variations of the equilibrium constants
with temperature and pressure were also calculated.
Figures 5.1 through 5.4 are plots of the output from the EQ3/EQ6 program.
Figures 5.1 and 5.2 show the variation 1n pH as a function of the lime and
sodium hydroxide added, respectively. When the solution pH reached 11.5, the
temperature was raised to simulate heating of the solution before stripping.
The temperature was changed from 25°C to 95*C with a corresponding drop in pH
due to changes in the values of the hydrolysis constants. Figures 5.3 and 5.4
show the sludge production as a function of lime and sodium hydroxide added,
respectively. The temperature change also is apparent in Figures 5.3 and 5.4
as a drop in the sludge production. The chemical dose required to adjust the
pH to 11.5 and the sludge produced at 25"C were interpolated from these
figures and are suirmarized in Table 5.3.
5.2.2 Cost Estimates
Process design and cost estimates were done using a spreadsheet. Inputs
included chemical quantity used, sludge produced (both given in Table 5.3),
wastewater flow rate, and unit costs for chemicals, energy, labor, fuel, and
construction. The project life and a rate of return were also used to allow
amortization of the construction costs. The final inputs were the
Construction Cost Indices, calculated by Engineering News Record (1988), one
for the year for which the estimate is being prepared and one for the year in
which the costs are based. The output is a listing of the yearly costs for
the unit processes over the project life.
67
-------
o-
o» -
¦ = PLANT 1
• = PLANT 2
a = PLANT 3
o = PLANT 5
18.0
12.0
6.0
9.0
15.0
21.0
3.0
0.0
Grams Lime Added
Figure 5.1.
Calculated pH for Plants 1, 2, 3, and 5 for lime addition,
1n grains of lime added per kilogram of solution.
-------
N
O-
Ol"
a»'
PLANT t
PLANT 2
PLANT 3
PLANT 5
to '
in ~
20.0
25.0
5.0
15.0
30.0
10.0
55.0
0.0
Grams NaOH Added
Figure 5.2. Calculated pH for Plants 1, 2, 3, and 5 for sodium hydroxide addition,
in grams of sodium hydroxide added per kilogram of solution.
-------
o
o-
= PLANT 1
= PLANT 2
= PLANT 3
= PLANT 5
in -
K>
cn ~
in-
m
o ^
o
o
o-
o
•n
0.0
15.0
12.0
9.0
18.0
6.0
21.0
3.0
Grams Lime Added
Figure 5.3. Calculated sludge production for Plants 1, 2, 3, and 5 for
lime addition, lyrams of solid per kilogram of solution)
-------
o
cn
~o o
3 K) "
C/l
¦ = PLANT 1
• = PLANT 2
a = PLANT 3
~ = PLANT 5
d+-
o.o
qu
25.0
15.0
10.0
20.0
5.0
30.0
35.0
Grams NaOH Added
Figure 5.4. Calculated sludge production for Plants 1, 2, 3, and 5 for sodium
hydroxide addition, (grams of solid per kilogram of solution)
-------
TABLE 5.3. SUMMARY OF CHEMICAL AND SLUDGE DATA
(Data are for 1 L of Wastewater)
Adjustment of pH to 11.5 With:
Lime NaOH
Plant Lime Added Sludge Produced NaOH Added Sludge Produced
(g) (g) (g) (g)
1 21 35 31 4.3
2 18 45 23 ,0.9
3 3.8 0.6 5.5 0.1
5 18 5.4 26 0
72
-------
Table 5.4 is a listing of the values, i.e. energy, cost, labor cost, etc.,
used in the analysis. These values are quotes or estimates and are meant to
be representative of the costs that may be incurred. However a site-specific
analysis should be performed using the actual costs along with those costs
mentioned above which have not been included in these analyses. Appropriate
safety factors should be employed as necessary.
The chemical costs were calculated on a yearly basis using the following
formula:
chemical costs (5/yr) = Q * dc * $c (15)
where
Q = wastewater flow rate
dc = chemical dose
$c = chemical unit cost.
The Capital Recovery Factor, CRF, is the fraction of the cost of an
expenditure that is realized each year. The CRF also accounts for the lost
interest income that would have been earned had the money been invested at the
chosen rate of return and not spent. The CRF can be calculated as follows:
CRF idilll— (16)
(1+i)
where
i = rate of return in decimal form
n = project life in years.
5.2.3 Process Design
The size of any particular wastewater treatment operation is determined by
the amount of material, either wastewater or sludge, it must treat in a given
time period. Typically, operation size can be reduced to one design value,
usually a volume or an area, which best represents the size and therefore the
cost of the process. The equations used to arrive at this value are given in
73
-------
TABLE 5.4. ASSUMED CONSTANT VALUES
Lime Cost
$70/dry ton
Alum Cost
$305/dry ton
Project Life
10 yr.
Rate of Return
9%
ENR Construction Cost Index (CCI) for 1988
4493.2
ENR Construction Cost Index (CCI) for 1978
2653.6
Energy Unit Cost
J0.03/KW-hr
Wage
$lfi/hr.
Detention Times:
Rapid Mix Tank
10 min.
Circular Clarifier
30 mi n.
Gravity Thickener
10 days
Dewatering Lagoon
30 days
Filter Press
10 min.
Depths:
Circular Clarifier
4 ft.
Gravity Thickener
4 ft.
Wet Sludge Solids Content
2%
Dry Sludge Solids Content
20%
Landfill Distance
40 mi.
Vacuum Thickener Loading Rate
2 lbs. solids/ft2/hr.
Fuel Cost
Jl/gal.
74
-------
Table 5.5. A further explanation of these equations or any of the unit
processes can be found in a water or wastewater treatment design text such as
Water Treatment Principles and Design (James M. Montgomery, Consulting
Engineers, Inc., 1985) or Wastewater Engineering Treatment, Disposal, Reuse
(Metcalf and Eddy, Inc., 1979). Table 5.6 lists the factors used for both
conversion between SI and English units as well as within any system of units.
5.3 RESULTS AND DISCUSSION
Tables 5.7 through 5.10 show the estimated yearly costs for the unit
treatment processes for Plants 1, 2, 3, and 5, respectively. Yearly costs for
each of the unit processes costs are shown for use of either lime or sodium
hydroxide to adjust the pH. Those processes denoted by represent the
lowest cost treatment system for chemical addition, mixing, sludge removal,
and sludge disposal based on the factors of this analysis.
In some instances when sodium hydroxide is used to adjust the pH, the
sludge production was negligible. Cost estimates for sludge thickening
processes in these instances have not been reported since the small size of
these units makes accurately estimating the cost difficult. In other
instances with sodium hydroxide, the sizes of various unit processes became so
large that costs could not be estimated with accuracy and again no cost
estimates have been reported.
For each of the plants, at any of the flowrates studied, the most cost-
effective treatment system was the same. This system consisted of lime
addition for pH adjustment, followed by precipitate removal with a clarifier
and sludge thickening in a dewatering lagoon, followed by disposal of the
dewatered sludge in the landfill. However, the high moisture content of
sludge in dewatering lagoons can offset some of the beneficial savings in
subsequent processes such as sludge handling and disposal.
The overall cost of this set of processes was relatively less than the cost
of any other combination of processes. Included in these estimates was
recalcitrating of the lime when higher doses are used (i.e. with 200,000 and
500,000 gallons of wastewater per day). The presence of heavy metal residues
in the sludge, which may be released to the atmosphere during the reducing
process, may prevent the reclamation of the lime due to environmental and
economic concerns. If so, the cost for chemical addition would increase,
75
-------
TABLE 5.5. DESIGN EQUATIONS
Chemical Feed Rate = Q * dc
Rapid Mix Tank Volume = Q * tr
Clarifier Plan Area = Q * tr / h
Gravity Thickener Plan Area = Q * tr / h
Vacuum Thickener Area = Q * pc / Lr
Dewatering Lagoon Volume = Q * tr
Filter Press Volume = Q * tr
Sludge Dry Weight = Q * Ps
Sludge Wet Weight = Q * Ps / Cs
where
Q = wastewater flowrate
dc = chemical dose
tr = detention time
h * depth
Lr = loading rate
p5 = sludge production
Cs = solids content
76
-------
TABLE 5.6. CONVERSION FACTORS
3.785 L/gal.
7.84 gal./ft3
8.34 lbs. water/ft3
2.2 lbs./Kg
1000 g/Kg
60 min./hr.
24 hr./d.
365 d./yr.
62.4 lbs. water/ft3
77
-------
TABLE 5.7. SUMMARY OF COST ESTIMATES FOR PLANT 1
(S/yr) '
Flowrate (gal/d)
50.000
100.000
200,000
500.000
Chemical:
Lime
122,000*
245,000*
489,000*
1,220,000*
Mixing Operations:
Chemical Feeder
Mixing Tank
29,000*
11,000*
33,000*
11,000*
27,000*
12,000*
32,000*
14,000*
Separation Process:
Clarifier
12,000*
12,000*
13,000*
17,000*
Thickening Processes:
Gravity Thickener
Vacuum Thickener
Dewatering Lagoon
Filter Press
121,000
250,000
18,000*
202,000
213,000
383,000
32,000*
171,000
383,000
637,000
62,000*
172,000
1,140,000
1,080,000
134,000*
200,000
Disposal Operations:
Dry Sludge Disposal
Wet Sludge Disposal
93,000*
871,000
157,000*
1,800,000
306,000*
3,850,000
917,000*
9,260,000
Chemical:
NaOH
718,000
1,440,000
(1)
(1)
Mixing Operations:
Chemical Feeder
Mixing Tank
31,000
10,000
146,000
11,000
(1)
(1)
(1)
(1)
Separation Process:
Clarifier
13,000
•146,000
(1)
(1)
Thickening Processes:
Gravity Thickener
Vacuum Thickener
Dewatering Lagoon
Filter Press
32,000
86,000
4,000
166,000
55,000
115,000
6,000
166,000
(IV
(1)
(1)
(1)
(1)
(1)
(1)
(1)
Disposal Operations:
Dry Sludge Disposal
Wet Sludge Disposal
26,000
97,000
37,000
231,000
(1)
(1)
il)
(l)
Notes: * Flags the most cost effective set of processes.
(1) The size of the unit became so large with given design
parameters that an accurate estimate of the costs could
not be made.
78
-------
TABLE 5.8. SUMMARY OF COST ESTIMATES FOR PLANT 2
($/yr)
Flowrate (gal/d) 50,000 100,000 200,000 500.000
Chemical:
Lime 96,000* 191,000* 383,000* 957,000*
Mixing Operations:
Chemical Feeder 27,000* 31,000* 24,000* 31,000*
*
Mixing Tank 11,000* 11,000* 12,000* 14,000
Separation Process:
Clarifier 12,000* 12,000* 13,000* 17,000*
Thickening Processes:
Gravity Thickener 55,000 274,000 378,000 2,890,000
Vacuum Thickener 284,000 445,000 737,000 1,390,000
Dewatering Lagoon 21,000* 38,000* 73,000* 167,000*
Filter Press 166,000 166,000 177,000 213,000
Disposal Operations:
Dry Sludge Disposal 108,000* 199,000* 386,000* 931,000*
Wet Sludge Disposal 1,100,000 2,240,000 4,380,000 1,125,000
Chemical:
NaOH 533,000 (1) (1) (1)
Mixing Operations:
Chemical Feeder 27,000 (1) (1) (1)
Mixing Tank 10,000 (1) (1) (1)
Separation Process:
Clarifier 12,000 (1) (1) (1)
Thickening Processes:
Gravity Thickener 21,000 (1) (1) (1)
Vacuum Thickener 58,000 (1) (1) (1)
Dewatering Lagoon 2,000 (1) (1) (1)
Filter Press 166,000 (1) (1) (1)
Disposal Operations:
Dry Sludge Disposal 19,000 (1) (1) (1)
Wet Sludge Disposal 41,000 (1) (1) (1)
Notes: * Flags the most cost effective set of processes.
(1) The size of the unit became so large with given design
parameters that an accurate estimate of the costs could
not be made.
79
-------
TABLE 5.9. SUMMARY OF COST ESTIMATES FOR PLANT 3
($/yr)
Flowrate (gal/d) 50,000 100.000
Chemical:
Lime 20,000* 40,000*
Mixing Operations:
Chemical Feeder 19,000* 24,000*
Mixing Tank 11,000* 11,000*
Separation Process:
Clarifier 12,000* 12,000*
Thickening Processes:
Gravity Thickener 18,000 24,000
Vacuum Thickener 59,000 64,000
Dewatering Lagoon 500* 2,000*
Filter Press 166,000 166,000
Disposal Operations:
Dry Sludge Disposal 8,000* 18,000*
Het Sludge Disposal 32,000 45,000
200.000
81,000*
27,000*
12,000*
14,000*
29,000
72,000
2,000*
166,000
21,000*
68,000
500.000
202,000*
30,000*
14,000*
17,000'
43,000
97,000
13,000*
166,000
32,000*
165,000
Chemical:
NaOH
Mixing Operations:
Chemical Feeder
Mixing Tank
Separation Process:
Clarifier
127,000
10,000
10,000
12,000
255,000
14,000
11,000
13,000
510,000
25,000
12,000
14,000
(1)
(1)
(1)
(1)
Notes: * Flags the most cost effective set of processes.
(1) The size of the unit became so large with given design
parameters that an accurate estimate of the costs could
not be made.
80
-------
TABLE 5.10. SUMMARY OF COST ESTIMATES FOR PLANT 5
(S/yr)
Flowrate (gal/d)
Chemical:
Lime
Mixing Operations:
Chemical Feeder
Mixing Tank
Separation Process:
Clarifier
Thickening Processes:
Gravity Thickener
Vacuum Thickener
Dewatering Lagoon
Filter Press
Disposal Operations:
Dry Sludge Disposal
Wet Sludge Disposal
50.000
96,000*
28,000*
10,000*
13,000*
40,000
92,000
4,000*
151,000
29,000*
146,000
100,000
191,000*
31,000*
11,000*
13,000*
61,000
127,000
7,000*
161,000
41,000*
102,000
200.000
383,000*
24,000*
12,000*
13,000*
91,000
181,000
11,000*
161,000
500,000
957,000*
31,000*
14,000*
•17,000*
173,000
321,000
26,000*
161,000
62,000* 133,000*
561,000 1,350,000
Chemical:
NaOH
Mixing Operations:
Chemical Feeder
Mixing Tank
Separation Process;
Clarifier
602,000
30,000
10,000
12,000
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
Notes: * Flags the most cost effective set of processes.
(1) The size of the unit became so large with given design
parameters that an accurate estimate of the costs could
not be made.
81
-------
possibly doubling. However, if recalcitrating is possible, many of the sludge
dewatering and handling costs would decrease. Estimates were based on
reclamation of lime from sludge, substantially decreasing the volume of sludge
to be treated.
A number of factors for which no information was available or no
representative price could be established may have a profound effect on the
relative cost effectiveness of these processes. For other inputs, estimates
were made from characteristics of municipal wastewaters. These estimates may
not be representative of the wastewaters generated by metal winning
facilities.
One factor that will govern the size, and ultimately the cost, of the
clarifier is the particle-settling velocity. The higher the settling
velocity, the smaller and less expensive the facilities. The cost estimates
are based upon settling velocities of municipal wastewaters treated with lime,
which may be on the same order of magnitude as those for industrial
wastewaters.
A second factor is the dewatering characteristics of the sludge. A sludge
in which the excess water is readily removed will require smaller dewatering
facilities than a sludge that tightly holds excess water. The design is based
upon characteristics of a typical municipal sludge, which will have a much
different dewaterabi1ity. The dewatering characteristics of the ammonia-
stripper sludge could be different and may require larger or smaller
facilities.
Another factor is the cost of the land necessary for each of the individual
processes. Gravity thickeners and dewatering lagoons are area- intensive
processes and will be least cost-effective in areas with high land values.
Since no land value was figured into this analysis, the land- intensive but
mechanically simple processes were favored over the mechanical processes such
as vacuum dewatering and the filter press. A reevaluation, considering land
costs for a specific site, may favor the use of other less land-intensive
processes.
The sludge disposal costs are estimates of time and material needs only and
do not include the actual cost-per-unit-volume for ultimate disposal of sludge
in a landfill. The cost of transport and disposal of sludge varies
82
-------
considerably based upon geographical origin of the waste, location of the
landfill, and classification of the waste (i.e. hazardous, radioactive,
nonhazardous, etc). Also, the disposal of unstabilized sludge regulated under
Title C of RCRA is likely to be prohibited in the future. Therefore, no
estimate of the cost of ultimate disposal or landfilling was made.
5.4 SUMMARY AND CONCLUSIONS
Cost estimates for the chemicals and equipment to adjust the pH of an
ammonia-bearing, metal winning wastewater prior to stripping show that lime
can be more economical than caustics for pH adjustment. In addition, the most
cost-effective method for disposal of the sludge solids generated was
dewatering in a lagoon followed by landfill disposal of the solids. However,
there may be a different set of cost-effective processes when costs for land,
transport, and handling of large quantities of sludge are high.
83
-------
6. QUALITY ASSURANCE/QUALITY CONTROL
The following additional analytical tests were performed or instrument
calibration was checked for QA purposes.
(a) Two aliquots from the same sample were submitted for chemical
analyses without indicating that they were duplicates. These samples
are from solution A (see Table 3.3).
Analytical results:
Concentration. nra/L
Percent
Soecies Sample A Sample A Averaoe Variation
Sulfate 22,000 25,500 23,750 ±7.4
Chloride 28,000 27,750 27,875 ±0.4
Magnesium 184 1B0 182 ±1.1
Sodium 19,000 20,000 19,500 ±2.6
Calcium <10 <10 <10
(b) Also submitted was a distilled water sample for chemical analysis.
Analytical results:
Spgcies Concentration. mq/L
Sulfate <4
Chloride <50
Magnesium <10
Sodium 11
Calcium <10
(c) Ammonia analyses: The ammonia electrode was calibrated everyday
using standard solution to assure that the slope did not exceed
-57 (±3) mV. Also, the instrument reading was frequently checked
after the ammonia analyses of test samples to assure that the
variation in accuracy did not exceed ±10 percent. Instrument
sensitivity was verified using two different sources of analytical
grade ammonium salts.
84
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(d) pH analyses: The pH probe was standardized using pH 4, 7, and
10 buffer solutions on the mass-transfer rate studies. If the
difference between initial and final solution pH exceeded 10 percent,
the experiments were repeated.
(e) The calibration information for thermocouples and flow meter is given
in the laboratory notebook. The flow meter readings were checked
with a laboratory in-line flow measurement and found that the flow
meter reading was within 2 percent of the average of 4 measured
values.
(f) Steam flowrate was measured at least three times for each setting of
the valve openings. The variation of measured steam flowrates at a
given opening did not vary by more than ±1.8 percent. The
calibration curve is given in Figure 4.6.
The performance audits for laboratory studies were conducted by the QA unit
of Battelle's Biological Sciences Technical Center and an external QA officer
appointed by the U.S. EPA.
85
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7. REFERENCES
Barrett, P. V. L. Gas absorption on a sieve plant. Ph.D. Thesis. University
of Cambridge, U.K. 1966. As cited in: P.V. Danckwerts. Gas-Lighted
Reactions, McGraw-Hill Book Co., NY. 1970.
Danckwerts, P. V. Gas-Liquid Reactions. McGraw-Hill Book Company, New York,
New York. 1970.
Engineering News Record, Market Trends, 220(22):40, 1988.
Gumerson, R. C., R. L. Culp, and S. P. Hansen. Estimating Water Treatment
Costs, United States Environmental Protection Agency, Municipal Environmental
Research Laboratory, Cincinnati, OH, EPA 600/2-79-162a and EPA 600/2-79-162b,
1979.
Kavanaugh, M. C. and R. R. Trussell. 1980. Design of aeration towers to
strip volatile contaminants from drinking water. Journal AWWA. December
1980.
McCabe, W. L., and J. C. Smith. 1984. Unit Operations of Chemical
Engineering, Third edition. McGraw-Hill, New York.
Metcalf and Eddy, Inc., Wastewater Engineering Treatment, Disposal, Reuse,
2nd. ed., McGraw-Hill Book Co., New York, 1979.
Montgomery, J. M., Consulting Engineers, Inc. Water Treatment Principles and
Design. John Wiley & Sons, New York. 1985.
Onda, L., E. Sada, T. Kobayashi, S. Kito, and K. Ito. Salting-out Parameters
of Gas Solubility in Aqueous Salt Solutions. Journal of Chemical Engineering
of Japan 3:18-24, 1970.
Patterson, J. W. Industrial Wastewater Treatment Technology, Second edition.
Butterworth Publishers, Massachusetts. 1985.
Perry, R. E., and C. H. Chilton, eds. Chemical Engineers Handbook, 5th ed.
McGraw-Hill, New York. 1973.
Powers, S. E. Optimization of an Ammonia Stripping Process for a
Semiconduction Manufacturing Wastewater. Master's thesis. Clarkson
University. 1985.
Treybal, R. E. 1980. Mass Transfer Operations. McGraw-Hill, New York.
Struzeski, Jr., E. J. Ammonia Stream Stripping at Miscellaneous Nonferrous
Metals Plants; Case Histories. In Proc. 33rd Industrial Waste Conference,
Purdue Univ., Lafayette, IN. p. 204. 1978.
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Wolery, T.J. Calculation of Chemical Equilibrium betwen Aqueous Solutionand
Minerals: The EQ3/EQ6 Software Package. Technical Report UCRL-52658,
Lawrence Livermore Laboratory, February, 1979.
Wolery, T.J. EQ3NR, A Computer Program for Geochemical Aqueous Speciation-
Solubility Calculations: UCRL-5314, Lawrence Livermore Laboratory, April,
1983.
Wolery, T.J. EQ6, A Computer Program for Reaction-Path Modeling of Aqueous
Geochemical Systems: User's Guide and Documentation. Technical Report UCRL-
53788, Lawrence Livermore Laboratory, April 1987. in preparation.
U.S. Environmental Protection Agency. Draft Development Document for Effluent
Limitations Guidelines and New Source Performance Standards for the
Miscellaneous Nonferrous Metal Segment of the Nonferrous Metals Point Source
Category, EPA-440/1-76-067. Effluent Guidelines Division, U.S. EPA,
Washington, D.C. 1976.
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TECHNICAL REPORT DATA
(Ttear rrad Incrructiont on «ht rtumr before compter
1. REPORT NO. 3.
EPA/600/2-91/046
«. TITLE ANDSUBTITLE
Bench-Scale Evaluation of Ammonia Removal from
Wastewater by Steam Stripping
ft REPORT DATE
September 1991
». PERFDRMINB ORGANIZATION CODE
7. ALTTMORIS)
G.B. Wyckramanayake, D.P. Evers, J.A. Klttel, and
A. GaJ/askar
» PERFORMING organization NAME and address
Batteflle Memorial Laboratories
Columbus Division
505 King Avenue
Columbus, OH 43201-1693
IB. PROGRAM element NO. " "
11. CONTRACT/sAanT NO
68-03-3248
12. SPONSORING AGENCY NAME AND ADDRESS
Risk Reduction Engineering Laboratory
Office of Research & Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE of report and period cove red
Final Report
14. SPONSORING AGENCY CODE
EPA/600/14
IS. SUPPLEMENTARY NOTES
Project Officer: John 0. Burckle
FTS 684-7506; (513)569-7506
16. ABSTRACT
The purpose of this study was to generate laboratory data to support the
development of wastewater discharge standards for ammonia in nonferrous metal
winning processes. The objective was accomplished by studying ammonia removal
from synthetically compounded "wastewater" samples using a bench-scale steam
stripping apparatus.
Although no significant variation of mass transfer rate coefficient (K) was
observed when S0% concentrations were varied from 5,000 to 20,000 mg/L, K was
the highest for low S0"4 wastewaters when pH was adjusted using NaOH.
Results of the steam stripping study indicated that varying chemical
constituents such as S0=4 and the molal strength did not have a significant
effect on the efficiency of ammonia removal. Higher removals (99.9 percent or
more) can be achieved by preheating wastewater and operating the stripping
tower at high steam-to-wastewater flowrate ratios such as 4 lb/gallon. Based
on engineering unit process and operation requirements, the cost analysis
indicated that lime may be more economical than caustic for pH adjustment,
depending upon waste sludge characteristics and disposal requirements.
17. KEY WOROS AND DOCUMENT ANALYSIS
a DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED terms
c. cosati Field'Croup
waste water, ammonia
wastewater discharge.,
ammonia removal,
steam stripping
it. Distribution statement
RELEASE TO PUBLIC
1». SECURITY CLASS (ThuXrpon/
Unclassified
11. NO. Of PAftK
20 SECURITY CLASS (Thnpu$n
Unclassified
«
22. PRICE
EPA F«nr 2230.1 (R>«. 4-7T>
i
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