PB84-127
Wasfce
and Recycle of
Illinois inst. of Tech., Chicago
Prepared for
Industrial Environmental Research
Lab.-Cincinnati, OH
Nov 83
-------
r.PA-600/2-&3-li4
November 1983
RECOVERY, REUSE, AND RECYCLE OF INDUSTRIAL WASTE
by
Kennath E. Noll
Charles H. Haas
Carol Schnidt
Prasad Kodukula
Department of Environmental Engineering
Illinois Institute of Technology
Chicago, II, 60G1G
Cooperative Agreement
CR 806819
EPA Project Officer
William A. Caw1ey
INDUSTRIAL ErjVIl-.011!!L,\7AL RESEARCH LABOPJVTOnY
OFFICE OF RESEAr.CH AND DEVEI.OPMrHI'
U.S. ENVIROHMEHTAL PROTECTION AGENCY
CIKCIHtlATI, OHIO 452C8
KPHOD'JUO C1
NATIONAL TECHNICAL
INFORMATION SERVICE
Ui DIP«RIM!N1 Of COwatRCt
SPRiNcnao. VA ::M
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TECHNICAL P.EPQHT DATA
(Please read Insirucnuiu on the rcrcrsc t>t!ure cornp
1. REPORT NO. |2.
EPA-GOO/2-83-114 |
4. TITLfc ANDSUSTITLE
Recovery, Reuse and Recycle of Industrial Wa=;te
7. AUTHOR(S)
Kcnnctli E. Noll, Charles N. Haas, Carol Schmidt and
Prasad Kodukula
9. PERFORMING ORGANIZATION NAME AND ADDRtSS
Illinois Institute of Technology
Chicago, Illinois 60616
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
'J.S. Environmental Protection Agency
Cincinnati, OH 45268
15. SUPPLEMENTARY NOTES
IcIiiiK! __
3 RECIPIENT 'S ACCESSION NO
PRa IL 1 2 7 I 4J
5. REPORT DATE
November 1983
6. PERFORMING ORGANISATION CODE
8. PERFORMING ORGANIZA1 ION REPORT
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVER
Id. SPONSORING AGENCY CODt
EPA 600/12
16. ABSTRACT
The major goal of this work is to produce a document useful in planning efforts aimed
elimination of industrial wastes through the application of recycle, recovery, and rev
technology. This goal was accomplished by collecting, reviewing, and evaluating infoi
mation pertaining to the State-of-the-art for recycle, recovery, and reuse of by-prodi
pollutants using different industrial waste treatment processes. From this infornatic
conclusions were made regarding the technological limitations associated with recycle,
recovery and reuse of industrial wastes.
The document provides an overview of the applications of the various processes to the
recovery of contaminants which may subsequently be recycled or reused.
The pollutants considered in this study are basically organic and inorganic by-product
from wastewater effluents, solid residue and gaseous emissions from industrial
operations. The first section contains chapters on methodology currently available fo
recovery of industrial and hazardous waste, and developing technology for recycle, reu
and recovery. The second section contains chapters on 5 technical categories, used fo
recovery namely, sorption, molecular separation, phase transition, chemical ntodificatii
and physical dispersion and separation.
,7 KEY WORDS AND DOCUMENT ANALYSIS
,i DESCRIPTORS
18 DISTRIBUTION ST -iTEMENT
b. IDENTIFIERS/OPEN ENDED TERMS
19. StCUFHTY Ci.ASS (This Kepurt/
20. SECURITY CLASS /Tills page)
c. COSATI 1 ioUI/Groiip
21. NO. OF PAGES
222
22. PRICE
EPA Foim 2220-1 (R«». 4-77) PREVIOUS EDITION is OBSOLETE .
1
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
This report is in partial fulfillment of the require-
ment of cooperative agreement CR 30G819-01 between
the Illinois Institute of Technology and the U.S.
Environmental Protection Agency. They v/ere developed
as part of the first year of the Industrial Waste
Elimination Research Center.
11
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ACKNOWLEDGEMENT
Funding for this study was provided by the U.S. Environmental Protection
Agency under Cooperative /-ercement No. CR 807859 to the Industrial Waste
Elimination Research Center (IWERC) a Consortium of the Illinois Institute
of Technology, Chicago, Illinois and the University of Notre Dame, South Bend,
Indiana.
IWERC is headquartered at Illinois Institute of Technology. Dr. James
W. Patterson, Chairman of the Pritzker Department of Environmental Engineering
is the Center Director. The mission of IWERC is to perform fundamental and
applied research on industrial waste elimination, reduction or avoidance by
recovery, recycle/reuse, and other methods of in-plant management.
Appreciation is expressed to Mr. William A. Cawley, Deputy Director,
Industrial Environmental Research Laboratory of the U.S. Environmental
Protection Agency and Chairman of the IWERC Policy Board.
111
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Table of ContenLs
Chapter
I
II
III
IV
V
VI
VII
VIII
IX
Section I
Scope of the Study
Industrial Treatment of Waste for Recovery,
Reuse, or Recycle
Resource Recovery From Hazardous Waste
Developing Technology For Recovery, Reuse
or Recycle
Section II
Sorption
Molecular Separation
Phase Transition
Chemical Modification
Physical Dispersion and Separation
Page
1.1
2.1
3.1
4.1
5.1
6-1.
7.1
8.1
9.1
IV
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CHAPTER 1
SECTION 1
SCOPE OF THE STUDY
1.1 INTRODUCTION
Increased emphasis has been placed on studies of the chemistry, biolo-
gical effects, treatment, fate, and control of industrial by-product pollu-
tants. Discovery of the presence of such materials at high concentrations
coupled with the recognition of their environmental impacts and potential
health hazards has led to major legislative efforts which would limit their
entrance into the environment. In addition, there is an increased interest
to ensure the continued viability of domestic minerals (which constitute
most of the raw materials for various industrial operations), minerals
economy, and the maintenance of an adequate mineral base. The environmental
regulations prohibiting the discharge of major pollutants from industrial
activities, coupled with the need for conservation of raw materials has led
to consideration of the recycle, recovery, and reuse of waste products. The
recycle, recovery, and reuse alternative is doubly advantageous since it
conserves a materials supply which is beginning to be recognized as finite
while reducing the quantity of hazardous pollutants discharged into the
environment.
The choice between recycle, Recovery and reuse of valuable materials
from waste and disposal of waste seenis to depend mainly on two factors;
economics and technology. Economics is probably the most important factor
that limits the recycle, recovery, and reuse of industrial by-products. The
high cost of recovering lev-value materials and the consequent relative
unprofitability seem to prevent several industries from adoption of .recycle
1.1
-------
or recovery techniques for waste by-products. The high costs of recycle or
recovery techniques, however, can probably be reduced by improving the present
day technology. Any such attempts would require the identification of tech-
nological limitations associated with th? recycle and recovery techniques.
So, it is necessary to collect, review, and systematically organize and eval-
uate information pertaining to the state-of-the-art for recycle, reuse and
recovery of by-product pollutants; the efficiency, energy, and resources
associated with these processes; and the future needs and demands for reduc-
tion, elimination, or reuse of the unwanted by-products. The execution of
these processes should result in a collection of information which defines
the limiting technology and the energy and economic constraints associated
with various techniques and processes, as well as their potential for future
development and expansion as valuable waste elimination methods. Such infor-
mation would be of use to focus future developments in the area of recycle,
recovery, and reuse technology sliced at the elimination of industrial by-
product waste.
1.2 OBJECTIVES
The major goal of this book is to produce a document useful in planning
future efforts aimed at the elimination of industrial wastes through the
application of recycle, recovery, and reuse technology. This objective was
accomplished by collecting, reviewing, and evaluating information pertaining
to the state-of-the-art for recycle, recovery, and reuse of by-product pollu-
tants using different industrial waste treatment processes. From this infor-
mation, conclusions were made regarding the technological limitations associ-
ated with recycle, recovery, ard reuse of industrial pollutants.
This study is not meant to provide detailed technical information on
the treatment process itself no elaborate discussions on the various
1.2
-------
applications of the processes. It does however, provide an overview of the
applications of the various processes to the recovery of contaminants which
may subsequently be recycled or reused.
1.3 ORGANIZATION OF THE BOOK
In this book, an attempt is made to suggest technological limitations
associated with unit processes currently or potentially employed for removal
of organic and inorganic pollutants from various industrial waste streams.
This goal was accomplished by collecting, reviewing, evaluating, and summa-
rizing information pertaining to the state-of-the-art for the recycle,
recovery and reuse of pollutants in industrial waste effluents.
The pollutants considers;' in this study are basically organic and
inorganic by-products from \\rastewater effluents, solid residue and gaseous
emissions from industrial operations.
The information collected during the course of this project is summarized
and presented under two sections. The first section of the uook consists of
chapters on the methodology currently available for recovery of industrial
and hazardous waste, and developing technology for recycle, reuse, and
recovery. The second section of the book contains chapters concerned with 5
technical categories, used for recovery namely, sorption, molecular separa-
tion, phase transition, chemical modification, and physical dispersion and
separation. This categorization is based on the type of transformation a
pollutant would undergo during the waste recovery in a given unit process or
operation.
It should be pointed out here that the categorization of unit processes
as done above, it .quite arbitrary and, needless to say, there might be some
overlapping.
1.3
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In each chapter in the second section individual unit processes are
presented with a brief discussion of the process itself, its applications,
and the technological limitations associated with the process. If a process
is used for removal of both organic and inorganic pollutants (for example,
ion exchange'), ics application and the technological limitations are dis-
cussed in thf: same chapter but under different sections for each type of
pollutant. A similar approach is adopted in the case of processes (for
example, adsorption) which are based on principles common for the removal of
pollutants from both gaseous and wastewater streams.
At the outset, each chapter deals with a process description. This
would include the underlying principles of the process, operating charac-
teristics, process configurations, and any unique features of the process.
A detailed technical analysis of each and every process was beyond the scope
of this book.
Immediately following the process description section, each chapter
discusses the limiting technology associated with the concerned treatment
i
process. Conclusions on technological limitations of the process for by-
product recovery and reuse are made based upon the literature gathered on
the process. Sincere attempts were made to make such conclusions as specific
i
as possible. One of the major problems encountered was the literature
I
pertaining to the processes and techniques employed in recovering industrial
by-products which were of a general and somewhat non-technical nature. It
was consequently difficult to make specific conclusions on limiting technol-
ogy based on available technical and performance data. As can be expected,
due to proprietary value, technical Information on industrial processes is
not as extensively available as it is in the case cf municipal wastewater
treatment prncps«
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The next section of each chapter deajs with application of eacli process
for pollutant removal and recovery from industrial waste streams. The types
of industries using "he process for pollutants removal are listed in this
section. In a number cf cases, recovery of by-products is not practiced.
It seems that very little technical data pertaining to the recovery of by-
products in real-life industrial situation arc.- available. In most cases,
even the process performance data are scarce due to the proprietory value of
the material. It is also possible that information on recovery of industrial
by-products is scant due to the fact that this area has received attention
only in recent years.
The last section of each chapter gives a list of the references used in
preparing the chapter.
1.4 WASTE CLASSIFICATION FOR RFCYCLE, RECOVERY AND REUSE
The quantity and quality of industrial wastes generated by various
industries is difficult to identify, however, Jennings (1982) has provided
an initial evolution by conducting a national industrial residual flow
study. Table 1.1 presents the rank order of industries producing residue.
Industrial residuals were defined as those residues that are routed either
to unique treatment technologies or to chemical waste disposal facilities
and considered "hazardous" under the Resource Recovery Act and The Toxic
Control Act. Current data indicates that these constitute about 40% by
weight of the total industrial discharge. The remaining fraction is composed
of such items as industrial trash, foundry sand, wool waste and slags.
The table shows that 75% of the residual volume is from the chemical,
primary metals, and fabricated metals industries.
Jennings was also able to estimate the percentage of residual material
1.5
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as to solids, liquid, or sludges as shown in Table 1.2. Under each category,
the residuals were identified by physical and chemical properties (Table 1.3).
These tables show that liquids and sludges are a large percent of the total
problem. This remains true even when the unidentified category is lumped
with the solids.
The miscellaneous special solids category contain wastes such as pesti-
cide solids and containers, explosives, pathogenic wastes, DOT "poisons" and
similar residues. The metal solutions and metal sludge categories contain
predominantly heavy metal residuals. The liquid categories contain both
dilute and concentrated solutions and (where appropriate) non-aqueous
liquids. Metals solutions and metal sludges accounted for nearly 15% of the
total.
1.5 METHODOLOGY
For the purpose of clarity, it is necessary to define the terror recovery,
reuse, and recycle. Recovery is defined as the extract of any pollutant from
wastes. The tjrms reuse and recycle described the manner in which the
recovered materials are put to Mse. Reuse of the material is its utilization
for any purpose, whether it is the same or different from its previous use.
Recycle will be defined as a specific type of reuse in which the recovered
material is reused for the same purpose as that for which it had been used
previously.
The effort for this book was divided into two different phases and a
summary of these phases is in order.
1.6
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TABLE 1.1
TOTAL QUANTITY OF INDUSTRIAL WASTE ORDERED BY MANUFACTURING INDUSTRIES
THAT PRODUCE HAZARDOUS RESIDUAL
INDUSTRIES
CHEMICALS
PRIMARY METALS
FABRICATED METALS
MACHINERY
PAPER
TRANSPORTATION
FOOD
PETROLEUM
STONE
ELECTRICAL
RUBBER
LEATHER
LUMBER
INSTRUMENTS
MISC. MANUFACTURING
FURNITURE
TEXTILES
PRINTING
TOBACCO
APPAREL
PERCENT OF ^
TOTAL QUANTITY '
37.6
29.1 74.4
7.7
6.5
4.6
4.0
2.7 22.9
2.4
2.0
0.7
0.7
0.5
0.4
0.3
0.2
0.2 2.6
0.2
0.1
<0.1
<0.1
TOTAL = 100% of 27.8 million tons of wastes reported from 21 states.
1.7
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TABLE 1.2
PERCENTAGE OF RESIDUAL TYPE IX
EACH LEVEL I WASTE CLASSIFICATION'
PERCENT OF
CLASSIFICATION TOTAL* IN CLASS
SOLIDS 13.9
LIQUIDS 54.4
SLUDGES 23.8
UNIDENTIFIED 7.9
*
Total «= 100% of 15.4 million tons of hazardous
wastes reported from 30 states.
1.8
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TABLE 1.3
PERCENTAGE OF RESIDUAL TYPE RY CHEMICAL CHARACTERISTICS
SOLIDS
PERCENT OF TOTAL IN CLASS
ORGANIC SOLIDS
INORGANIC SOLIDS
MISCELLANEOUS
SPECIAL WASTES
11.8
28.0
60.2
LIQUIDS
HALOGENATED ORGANICS
NON-MLOGENATED
ORGANICS
ACIDS
CAUSTICS
METAL SOLUTIONS
OILS & OILY WASTES
MISCELLANEOUS
LIQUIDS
SLUDGES
PERCENT OF TOTAL2
1.0
8.6
34.8
18.8
11.4
7.6
17.8
PERCENT OF TOTAL3
IN CLASS
IN CLASS
ORGANIC SLUDGES
INORGANIC SLUDGES
METAL SLUDGES
41.8
33.5
24.7
1. Total = 100% of 2.1 million tons of hazardous wastes reported from 21
states.
2. Total = 100% of 8.2 million tons of hazardous waste." reported from 23
states.
3. Total = 100% D£ 3.6 million tons of hazardous wastes reported from 19
states.
1.9
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1.5,1 Phase I. Literature Collection
This phase consisted of a thorough collection of literature dealing
with information on technology whicli lias or may have appli cation in the
ureas of recycle, recovery and reuse of by-product wastes as well as informa-
tion directly related to the industrial by-product materials themselves.
The literature search was approached with the following basic questions
in mind: (1) Whar: wastes are presently produced as industrial by-products?
(2) What methods can be applied to these wastes to bring a! out their elimina-
tion through recycle, recovery and reuse?
Many sources are available which contain information pertinent to the
project, and the tools to facilitate its collection. Sources include jour-
nals, reports, hooks, and the proceedings of conferences and symposia. In
order to amass the largest collection of relevant information in the short
period of time available, it was necessary to make use of on-line computer
li-*rature searches, published literature searches, collections of abstracts,
and the literature reviews which appear periodically in certain journals.
On-line computer literature searches (for example, The EPA Computerized
Literature Search System) were used to access data bases and provide
bibliographic information in response to specific questions. Published
literature searches such as those produced by The National Technical Informa-
tion Service (NTIS) were valuable during the course of the project.
Over 1,200 abstracts concerning recycle, recovery and reuse were collected
from the Engineering Index.
1.5.2 Phase II. Literature Categorization
During this phase, the abstracts collected from Phase I were reviewed
and articles relevant to the project objectives werp collected. Information
1.10
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collected from computer searches and published bibliographies v;cre carefully
reviewed and pertinent articles obtained.
A review of collected literature indicated that the categorization of
literature can be based upon one of the three following approaches: a) an
industry-by-industry, b) process-by-process, c) material-by-material.
An industry-by-industry approach would have required a classification
of industries and their respective wastes and an evaluation of the several
possible methods by which these wastes could be treated. It seemed that
several industries using a given treatment process had similar technological
limitations in terms of recovery of their by-product pollutants. So the
same conclusions on limiting technology would have to be repeated for a
number of industries for a given treatment process.
If the literature categorization had been based on materials, the waste
by-products would require initial identification followed by studies of
various processes suited for their recovery and reuse. A careful evaluation
of the collected literature indicated that the limitations of technology are
more dependent upon the treatment process itself than on the type of \vaste
or type of pollutant treated. It was therefore decided that for the purpose
of this project the categorization of literature would be based on treatment
processes.
A schematic of literature categorization used in this project is shown
in Figure 1.1. The literature was broadly divided into throe major areas;
air, water, and solids, each of which deals with two major classes of by-
products, namely, organics and inorganics. After the collection of the
majority of material required by the project had been accomplished, the
following tasks were carried out.
1.11
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FIGUFE 1,
LITERATURE CATEGGRIZAT!ON
AIR
WATER
.-SOLIDS
SORPUON
ORGAN ICS - INORGANICS'
Y
— AREAS--OF TECHNOLOGY
MOLECULAR
SEPARATION
PHASE
CHEMICAL
ELQJllEKAIM
PHYSICAL
DISPERSION
AND J'
SEPARATION
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A total of 18 processes which are believed to have the tuost wide-spread
application in terms of removal and recovery of industrial by-products were
selected for study in this project. A list of the processes is presented in
Table 1.4. These processes are divided into five groups, depending upon the
type of transformation the by-product would undergo during the watte treat-
ment in a given unit process or operation. As mentioned earlier, the five
groups of processes are: sorption, molecular separation, phase transition,
chemical modification, and physical dispersion and separation.
After the identification of the unit processes listed in Table 1.4, a
research specialist was assigned to a unit process. Each treatment process
was evaluated according to the following outline:
I. The Process
II. Limiting Technology
III. Recycle, Recovery, and Reuse Applications
IV. References
It should be pointed out here that the references given at the end of
each chapter are listed in alphabetical order. Attempts were made to obtain
as many references as possible from recent years. The references are classi-
fied into four categories:
1) Titles read: Only the titles of the articles were read for the
references under this category. No attempts to obtain the abstracts
or the original articles were made.
2) Abstracts read: Under this category of references only the ab-
stracts of the articles were read.
3) Articles read: In this case the original articles were read.
4) Articles referenced: The articles listed under this category are
actually referenced in the text.
1.13
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TABLE 1,4 TREATMENT PROCESSES SELECTED
SORPTION
ABSORPTION
ADSORPTION
MOLECULAR
SEPARATION
REVERSE OSMOSIS
ION EXCHANGE
PHASE
TRANSITION
DISTILLATION
EVAPORATION
CHEMICAL
MODIFICATION
CHEMICAL REACTIONS
THERMAL REACTIONS
PHYSICAL
DISPERSION
AND
DEWATERING
FILTRATION
ULTRAFILTRATION
CONDENSATION CEMENTATION
REFRIGERATION
FLOTATION
DROPLET
SCRUBBING
EMULSION
LIQ-LIQ
EXTRACTION
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The references listed under the first three categories are not always
quoted in the actual text portion of the chapters. These are, however, in-
cluded in the references section of each chapter because it was felt that
they are related to the information presented in the text and the reader tay
refer to these, if interested,
1.6 SUMMARY AND CONCLUSION
In this study an attempt was made Co collect, review, and systematically
organize and evaluate information pertaining to the :>tate-cf-the-art for
recycle, reuse, and recovery of industrial pollutants through the use of
various waste treatment processes and to suggest technological limitations
associated with these processes.
At the present time, economics seems to be considered a raajor factor in
deciding if recycle, recovery and reuse of industrial pollutants are worth-
while. Needless to say, current^economic costs do not include the 'hidden*
coPts to society of environmental pollution and depletion of natural re-
sources. However, if the waste treatment technology is improved to a level
where economics does not become the limiting problem, recycle, recovery and
reuse of industrial pollutants would become feasible.
Generally, most of the processes discussed in this report are well-
developed and proven to be successful for effective removal of pollutants
they are designed to treat. However, a majority of processes are not either
economically or technically effective for recovery of by-product pollutants.
For example, precipitation is an effective process for removal but not for
recovery of heavy metals. A majority of industrial wastes receive precipita-
tion treatment but in most cases the resulting sludges are disposed of with-
out recovery of metals because of economic constraints.
1.15
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In the case of processes such as evaporation, there seem to be no insur-
ir»untable technical problems, however, operation;)! difficulties, such as
crystal formation and scaling seen to limit the recovery application of the
process In various industrial operations.
Scrr.o of the processes (e.g., cementation) studied in this project are
at an infant stage while sorae others are very well developed (e.g., activated
carbon). In the case of cementation, although the process is well developed
and conmonly used in hydronetallurgical operations, it has not been tested
on pilot and full scale at a. nuraber of nunicipal waste treatment facilities.
However, its application to industry to date has been limited and there is a
large scope foi research in this area. Even though major advances have been
made in the area of activated carbon technology, fundamental research on
adsorption/desorption mechanisms is warranted, which would lead Co improved
removal and recovery of organic and inorganic compounds.
As trencioned earlier, the second section of this report presents a
discussion of several v«iste treatment processes, their application to
industrial operations, and the technological limitations associated with the
respective processes. A brief summary of the information contained in the
section and the conclusions drawn from it are presented in a process by
process order below.
The unit processes considered under the category of sorption are highly
developed for removal of organics and inorganics from both gaseous and
wastewater effluents. The process of absorption for removing and recovering
gaseous pollutants seems to be most efficient when the pollutants are quite
soluble in the absorbent and when the absorbent is relatively non-volatiie,
non-corrosive, and has low viscosity. The rates of mass transfer between
1.16
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the gas and the absorbent are primarily determined by the amount of surface-
area available for contact. The contact, between the gas and liquid solvent
are most commonly achieved in plate und packed towers. Absorption of pollu-
tants (such as phenolic compounds, hydrocarbons, II,S, S0?, etc.) followed by
desorpcion constitutes a cyclic operation which allows reuse of the sorbent
and acts as a device for separation and concentration of the selected gas.
The process of adsorption in the area of air pollution is used for
removal of odors, hydrocarbons, Hg, S0?, and NO. The principal adsorbents
are activated carbon, silica gel, activated alumina, and synthetic zeolites.
In the recovery of organic gaseous pollutants, activated carbon has been by
far the most effective adsorbent used. The recovery of organic cocpounds
after breakthrough has been reached is generally achieved bv stripping. The
conventional nethods of regeneration of air pollutants involve heated air,
heated inert gas or heated steasi whereas thermal reactivation, steam regenera-
tion, and acid or alkaline regener.it ion are used for recovery of organics or
inorganics fron adsorbates used in wastcwater ircatr.ent.
The technological limitations associated with sorption process arc
summarized in Table 1.5.
TABLE 1.5 LIMITING TECHNOLOGY .FOR SORPTION rROCES_Sr.S
ABSORPTION:
SOLUBILITY OF CAS IM THE LIQUID
ADSORPTION':
UNDERSTANDING OF FUNDAMENTAL MECHANISMS OF
REMOVAL
REGENERATION PROCESSES
LACK OF COMPREHENSIVE PREDICTIVE MODELS
Of the three processes considered under molecular separation, ion-
exchange is a well established process and has been used in industrial
1.17
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operations for a long time whereas the. menbrane processes such as reverse
osmosis and ultraf iltri,tion have received attention only in recent years.
During the process of ion exchange, undesirable ions from a waste slrea:,;
are transferred on to the ion exchange material, such as synthetic resin,
which nay be regenerat
-------
The processes considered under the category of phase transition are eva-
poration, distillation, condensation and refrigeration. The first two pro-
cesses are used for the removal and recovery of waBtewater pollutants whereas
the latter are for gaseous pollutants. In metal and plastics finishing in-
dustries and, particularly the electroplating industry, closed-loop recycling
of wastes is achieved by using evaporation as a recovery process. Evaporation
is a very costly process, however, it becomes cost-effective as the concen-
trations of pollutantf; in the wastes increase and the flow rate becomes low.
Multiple-effect evaporators are more common in *-he electroplating industry
because of their relatively lower costs.
Distillation is a process in which the vaporization of a liquid mixture
yields a vapor phase containing more than one component. As a unit operation,
it has been used successfully either singly or in combination with such
operations as direct condensation, adsorption, and absorption for the recovery
of organic solvents. Distillation has many applications for compound recovery
from industrial wastes. The regeneration of activated carbon nay result in
a liquid which is distillable for recovery of the organic component. Other
applications include recovery of methylene chloride from polyurethane waste,
the recovery of organlcs from plating wastes, and the recovery of waste
solvents for reuse in cleaning industrial equipment.
The condensation process is employed by chemical process industries to
recover solvents and products which can be recycled to manufacturing process-
es, and is also used to recover volatile hydrocarbons from fuel-storage
operations. It employs either contact or non-contact methods for cooling a
vapor to the point where the partial pressure of the condensibie component
equals its vapor pressure. Less commonly, the temperature of the system is
1.19
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held constant and the system pressure is increased until the component's
partial nressure equals its vapor pressure.
The production of cooling or heat withdrawal, may be accomplished by
the solution melting, or evaporation of a substance, or by the extension of
a gas. The term refrigeration refers particularly to cooling below atmo-
spheric temperature. Refrigeration is one of several competing methods
for recovering emissions from bulk liquid transfer and storage operations,
and has been promoted for vapor recovery at gasoline loading racks.
Table 1.7 presents the technological limitations of processes
considered under the category of phase transition.
TABLE 1.7 LIMITING TECHNOLOGY FOR PHASE TRANSITION PROCESSES
EVAPORATION:
CRYSTAL FORMATION, SALTING, SCALING, CORROSION
ENTRAINMENT, AND FOAMING
DISTlLLftTIOM:
ENTRAINMENT EFFECTS ON ATTAINABLE PURITY
CONDENSATION:
LOW REMOVAL EFFICIENCY AT LOW LEVELS OF
CONDENSIBLE VAPORS
FOULING OF HEAT EXCHANGE SURFACES BY
PARTICULATF.S
Chesical precipitation and reduction are most commonly used to
remove and recover metals from industrial waste effluents. Whereas the
former process is used by a number of industrial operations to remove
various heavy metals, chemical reduction is mostly used to reduce hexavalent
chromium to its trivalent form in the plating and tanning industries.
The reduction process in this case is followed by precipitation of
trivalent chromium with either lime or sodium carbonate,
1.20
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Chemical precipitation and reduction are ir.ost commonly used to rcinovo
and recover metals from industrial waste effluents. Whereas the former pro-
cess is used by a number of industrial operations to remove various heavy
metals, chemical reduction is mostly used to reduce hexavalent chromium to
its trivalcnt form in the plating and tanning industries. The reduction
process in this case is followed by precipitation of trivalent chrcrv.ium with
either lime or sodium carbonate.
The cementation process, which is widely used in hydromctallurgical
operations, is not well developed for the removal and recovery of metcil.s
from industrial waste streams. In this process, the ioniacd metal in
solution is converted to its elemental stage by spontaneous electrochemioal
reaction through oxidation of another elemental metal which is also kept in
solution. The process performance cart be predicted in terms of electrode
potentials. This process is presently in its infant stage and there seems
to be a large scope for research and full-scale application in this area.
Catalytic hydrogenation is a useful method for achieving controlled
transformation of organic compounds. Using this technique it is possible
to saturate organic compounds with hydrogen. Catalytic liytirogenation has
been applied in the production of substitute natural gas having a high
concentration of methane and ethane. It has also been used to recover
hydrogen gas, and to convert the sulfur present in tail gas to hydrogen
sulfide which can undergo conversion to elemental sulfur.
A summary of technological limitations associated with the processes
involving chemical modifications of pollutants treated is presented in
Table 1.8.
The last category of unit processes considered in this study is physical
1.21
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TABLE 1.8 LIMITING TECHNOLOGY FOR PROCESSES INVOLVING CHEMICAL
MODIFICATIONS
CEMENTATION:
- NOT EFFECTIVE FOR LARGE FLOWS DUK TO LONGER
CONTACT TIMES REQUIRED
- EXCESS IRON CONSUMPTION RESULTING IN EXCESS
IRON SLUDGE REQUIRING DISPOSAL
- THERMODYNAMIC LIMITATIONS FOR ACHIEVING THE
DESIRED LOU LEVELS
PRECIPITATION:
- PRESENCE OF COMPLEXING AGENTS
- ACHIEVING OPTIMAL REMOVALS FOR MORE THAN
ONE METAL AT ONE pH
REDUCTION:
- HARD TO ACHIEVE INTIMATE CONTACT BETWEEN THE
REDUCTANT AND THE POLLUTANT, ESPECIALLY IN
CONCENTRATED HASTES
- INTRODUCTION OF NEV/ METAL IONS WHICH NEED
FURTHER TREATMENT FOR REMOVAL
PYROLYSIS:
- LACK OF UNDERSTANDING OF EFFECTS OF PROCESS
VARIABLES ON PROCESS PERFORMANCE
CATALYTIC HYDROCENATION:
- RATE OF CHEMICAL REDACTION
- RATE OF HYDROGEN TRANSPORT
1.22
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dispersion and separation. All the unit processes included in this category
(except liquid-liquid extraction; are used for removing suspended matter from
wastevater or gasc-ous streams.
Filtration is a physical process in which solids suspended in a gaseous
or a liquid stream are separated by passage through a previous medium that
separates and retains either on its surface or within itself, the solids
present in the suspension. In all filtration processes, a pressure differ-
ential is induced across the medium to force the gaseous or liquid stream to
flow through it.
In the case of filtration of liquids, either surface filters in which
the solids are deposited on the upstream side of the medium, or deep bed
filters, which deposit solids within the medium, are used. Surface filters
are normally used for suspensions with more than 17, solids whereas dilute
suspensions are treated by deep-bed filters. A wide variety of filtration
devices are commercially available.
The filter media used for liquid filtration may be a filter cloth,
filter screen, a layer of granular media such as sand, lake, coal, or
porous ceramics or a barrier composed of a disposable material such as
powdered diatomaceous earth or waste ash. Filter media used for filtration
of gases may be porous paper, iwoven and felt fabric filter, or gravel or
sand aggregate bed. Filtration has been used ^cr removal of suspended
matter from innumerable types of industrial wastewaters and gaseous streams.
Multi-ne'.'.ia filtration is commonly used for removal of the metal precipitates
from wastewater after it has been subjected.
Flotation is a unit operation used to separate solid or liquid particles
from liquid phase. In this process, fine air bubbles which are introduced
1.23
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into the liquid phase .ittnch to the particulnte matter and, consequently, the
buoyant force of the combined particle and ',\zs bubbles becomes lar^e enough
to cause the particle to rise to the surface. Three methods of introducing
gas bubbles are available: dissolved air flotation, air flotation and vacuum
flotation.
The technological limitations associated with processes under the cate-
gory of physical dispersion and separation are presented in Table 1.9.
The process of liquid-liquid extraction involves separating the compo-
nents of a liquid-liquid mixture by the addition of another liquid referred
to as the solvent, which is immiscible (or only partially miscible) with
the initial phase. The- solvent is chosen so that one or more of the compo-
nents of the original solution will transfer preferentially into the solvent
phase leaving the others behind in the so-called raffinate. The major
applications of this process in waste-water treatment engineering are 1)
recovery of phenol and i'olatec! compounds from waste-waters and 2) removal of
water soluble solvents such as alcohol Crora wastes containing mixed chlori-
nated hydrocarbon solvents.
1.24
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TABLE 1.9 LIMITING TECHNOLOGY FOR PHYSICAL DISPERSION o SEPARATION
PROCESSES
FILTRATION:
- LACK OF UNDERSTANDING OF PARTICLE/FILTER
INTERACTION
- MAINTENANCE OF FILTER IN GOOD CONDITION
LIQ-LIQ SEPARATION:
- SELECTION' OF SOLVENTS AND CONTACTORS TO
PRODUCE DESIRED RESULTS
1.25
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KKFtRFNTES
Jennings, A.A., "Analysis of The National Industrial Residual Flow I'robli-m,
IWERC Project 8001, 1982.
1.26
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ClIAl'TKK 2
SECTION 1
INDUSTRIAL TREATMENT OF WASTE FOR KfX'OVKKY, REUSE OP. RECYCLE
2.1 INTRODUCTION
Treatment of waste for recycle, recovery or reuse may be chemical or
physical and may consist of a sequence of operations. A list of separation
methods for liquids and solids is provided in Tables 2.1 and 2.2. The list
has ":>een divided into chemical and physical methods and is only an exanple of
the possible methods that can be combined to recover material. Recoverable
caterial may exist in the waste stream in many different forms, for example,
as metals or netal oxides. They may exist as acid solutions of metal salts.
Therefore, the selectJon of a recycle process depends on specific character
of the waste and requires careful consideration. For the purposes of this
work, technologies were grouped by their similarities and r/ot by their
ability to accept similar wastes.
2.2 INDUSTRIAL I'OLIA'YION UKCOVLKY
EPA funded a stuiJy of alternatives to conventional pollution control
that Involves recycle, recovery, and reuse (HK1, 1980). Twenty-five case
reports obtained froa the pollution control literature for the 1974-1979
period are summarized. The cases come from 11 industries, domestic as well
as foreign operations, and from small as well as large companies and one
public sanitary district. A roughly equal number of cases deal with pre-
dominantly water- and with predominantly air-related cases. Half the cases
involve process modification; the rest involve other types of optimization
approaches. Host of the pollution control by process change take place in
the process-intensive industries, as might be expected—chemicals, paper,
2.1
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Table 2.1 TREATMENT METHODS FOR LIQUID EEFLUENT
Chemical treatment methods
Example
Absorption
Cementation
Chlorination
Uerculsification
Electrolytic processes
Hydrolysis
Incineration
Ion exchange
Neutralisation
Oxidation
Precipitation
Reduction-
Piiysical treatment methods
Absorption
Crystallisation
Distillation
Evaporation
Filtration
Flotation
Foara fractioriation
Phase separation
Reverse osmosis
Solvent extraction
Stripping
Solvent recovery
Copper recovery
Cyanide oxidation
Soluble oil recovery
Metal recovery
Cellulose waste
Waste oils
Metal recovery
Waste acid
Phenol removal
Metals
Hexavalent chromium
Removal of volatile organics
Recovery of Inorganic salts
Solvent recovery
Sulphuric acid recovery
Sewage sludge
Dairy wastes
Metal separation
Oily wastes
Desalination
Metal recovery
Ammonia removal
2.2
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Table 2.2 TREATMENT METHODS FOR SOLIDS WASTE
Chemical treatment methods
Examples/comments
Calcination
Chlor'.nation
Cooking
Froth flotation
Leaching
Sintering
Physical treatment methods
Centrifugation
Comminution
Drying
Granulation
Magnetic treatment
Screening
Gypsum
Tin removal
Inedible offal
Coal recovery
Glass
Gives an aqueous solution which
may be treated as a liquid waste
(Table ?..i)
Colliery spoil
Millscale
Aniraal oil separation
De-oiling swarf
Mining wastes
Cars
Filter cake
Slag
Iron removal frora
Clinker
2.3
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petroleum, metals, and food.
The common characteristic of the alternative approaches is changed
in the production process resulting in the elimination rather than the
control of pollutants. Wherever pollutants can be eliminated—through
changes in the production process, recycling or reuse of captured wastes,
recirculatio •. of streams, or some other strategy—the need for and the
substantial costs of terminal treatment systems are avoided or minimized.
Identifying characteristics of alternative approaches Involve:
1. Recovery and reutilization of waste materials in the process
itself, in the production operations that the system serves, or in
an unrelated operation;
2. And/or energy conservation components based on overall design,
utilization of process heat, energy generation from waste combustion,
or combinations of these;
3. And/or use of substitute raw materials in the production process
upstream of the "alternative system" in order to make the system
more effective;
^. And/or modification of the production process for the same reasons.
Based on the 25 cases selected, seven categories of innovation accommo-
date all the cases reviewed. These are shown below:
New device
New procedure
New process
Modified process
Process chemical change/elimination
Fuel substitution
Other waste utilization
The largest number of cases involve process modification and changes in
process chemicals, but process chemical change/elimination, in this sampling
of cases, tends to be linked to other techniques. Fuel substitution, in
every case, involves the use of plant or process wastes as a fuel; if this
category is combined with other cases of waste utilization, it becomes the
2.4
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second most common category. In a large proportion of cases (23 of 25),
benefits were reportedly realized in two or more categories. In all but one
case, the costs of the innovation were lower than the conventional solution
by terminal treatment system. An overview of the cases is presented in Table
2.3 showing the technique or techniques used and the benefits achieved. Six
of these cases resulted in recovery or recycle of material and provide a good
example of the diverse nature of the technology.
1. Fiber recovery. In this case a manufacturer of corrugating medium
launched a campaign to capture and to reuse rejected fibers from four differ-
ent operations. In each case, rejected fibers were captured, reprocessed,
and reintroduced into the process at different stages. Resulting final
products were tested to determine whether or not the addition of rejects
adversely affected product quality. In the production of corrugating medium,
waste fibers cause fewer problems} than in fine paper or Kraft specialty
production.
2. Recovery of steel plant sludges. Large quantities of water are used in
hot strip rolling mills in the steel industry for removing fine scale from
the metal in forming. Very fine oxides, together with hydraulic oils and
lubricating greases released in rolling operations, enter the flume beneath
rolling operations with the wat^r. The very fine particles of oxide are
coated with oils and greases, and since small size means more surface area
per unit of weight, the metals are very contaminated. The oxides are too
fine for direct recharging to furnaces and need to be agglomerated by sinter-
ing. The heat of sintering causes the oils and greases to vaporize but is
insufficient to burn then, hence these hydrocarbons deposit on air handling
equipment, collect dust, and increase maintenance costs. Particulate air
2.6
-------
pollution control devices also cannot tolerate these- oils. For these reasons,
iron oxides occurring in rolling operations are not widely used and must be
disposed of as sludge.
The recovery process is a multi-stage process for reclaiming oil-free
oxides and recovering the oils. Only around 3 percent of the original
sludge is disposed of as waste. The sludge undergoes successive separation
and washing cycles; oils and greases are washed from the particles and later
separated from the wash solution; oxides are screened into coarse and fine
grades.
The system produces a product with 31 percent higher iron content than
Mesabi Range Fines and 15 percent higher than Marquette Range pellets. Costs
of recovery substantially lower than the cost of raw ores or pellets are
claimed.
3. Recovery of pickle liquors. An 85,000 ton/year stainless steel annealing-
pickling line used Nitric hydrofluoric acid in the- pickling operations.
Spent pickle baths were neutralized with lime, dewatered, and disposed of—
with loss of all the acid and pollution problems attending sludge disposal.
The recovery is accomplished by liquid-to-liquid extraction using an
organic solvent, TEP, at a 75 percent concentration in kerosene. The solvent
forms adducts with monobasic acids. The acids are stripped from the solvent
with water and the solvent is reused. Sulfuric acid is added to increase
acid yield. The metal sulfate by-products are neutralized before disposal.
The process recovers about 95 percent of the acid used; as a consequence
of the regeneration process, overall acid usage has dropped by 47 percent.
4. Sulfur and energy recovery. In this case the company faced the need to
reduce substantially S0_ levels and odors from a sulfite mill. SO- was
2.7
-------
emitted from a vent of the spent sulfite liquor evaporator and from the blow
tank receiving gases from the digester at intervals of two hours.
The company solved its problem by ducting evaporator SO,, emissions
directly to the mill's acid plant wet scrubber and by absorbing blow tank SO
emissions directly in the acid plant. To deal with the blow tank emissions,
the company installed a system for cooling and condensing blow tank off gases
ahead of absorption in an absorption tower and for recovering heat from the
digester blow as an adjunct to gas cooling. Recaptured SO- is reutilized in
the mill.
5. Air pollution reduction. This is a case where an inefficient system was
designed by the original manufacturer to reduce partlculate air pollution and
to recover energy. The process involved the handling of corrugated board
scrap. Waste materials were shredded and then conveyed pneumatically to a
roof-mounted cyclone separator over a baling operation. The system created
dust, and plant air was exhausted to the atmosphere. The cyclone was sealed
and equipped with a dust filtering device. The captured dust is conveyed
automatically to the baling system. Filtered air is returned to the plant,
and the incoming air volume is adjusted to the operation of the scrap handling
system. Incoming makeup air is now heated by spent steam from corrugating
machines, heat which had been ve^';ci previously.
6. Metal Recovery. A 130 tons per day incinerator was built to destroy
plant waste and sludge, produce energy, and recover silyer. The plant started
operations in 1976; it had been under development for nearly eight years.
The system receives waste from four manufacturing plants, a large office
building, and an educational campus. Solid waste is shredded and separated
into a light and heavy fraction. The light fraction is burned in a waterwill
2.8
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incinerator; combustion is augmented by burning fuel oil. Flue gases are used
to dry sludge generated in a wastewater treatment plant before being burned.
Steatn generated in the incinerators is used in a turbine to produce electrical
power.
Bottom ashes from the system and from the electrostatic precipit;>tor are
processed further to obtain silver. Silver is introduced into the system by
waste film generated in the production operations.
As these cases illustrate, recovery, reuse, and recycle approaches take
many technical forms—the use of new or modified devices and equipment; new
processes that replace or augment existing processes; the codification of
existing processes by a variety of techniques including changes in raw
materials, the elimination of or change in process chemicals, capture and use
of waste heat, recovery -jf. solvents, cleansers, and a variety of raw materials,
and the substitution of wastes for purchased fuels.
2.3 INDUSTRIAL WASTE WATER RECYCLE
A study conducted at Argonne National Laboratory (Kremek, 198.1). identi-
fied the technology presently used to allow reuse of vatewater from 3oiv.c major
industrial categories. The technology available to recovery material iron the
metal plating and iron and steel industries provide good illustrations as
follows:
1. Electroplating
Wastewater from plating processes comes from cleaning, surface prepara-
tion plating, and related operations. The constituents in this wastewater
include the basic material being finished as well as the components in the
processing solutions. Predominant among the wastewater constituents are
copper, chromium, nickel, zinc, lead, tin, cadmium, gold, silver, and platinum
2.9
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metals, as well as ions that occur from cleaning, surface precipitation, or
processing baths such as phosphates, chlorides, and various metal-complexing
agents.
Wastcwater from metal finishing processes comes from cleaning, pickling,
anodizing, coating, etching ami related operations. Predominant among the
wastewater constituents are ions of copper, nickel, chromium, zinc, lead,
tin, cadmium and ions that occur in cleaning, pickling, or processing baths
such as phosphates, chorides and various metal completing agents.
Table 2.5 lists the variations in wastewater characteristics found by EPA
in its survey of the electroplating industry. The table shows variation
between plants as well as within each plant.
Table 2.5 Comparison of Raw Waste Streams
from Common Metals Plating
Constituent Range (r.ig/1)
Copper 0.032- 272.5
Nickel 0.019-2954
Chromium:
Total 0.088- 525.9
llexavalent 0.005- 334.5
Zinc 0.112- 252.0
Cyanide:
Tdtal 0.005- 150.0
Amenable to chlorination 0.003- 130.0
Fluoride 0.022- 141.7
Cadmium 0.007- 21.60
Lead 0.663- 25.39
Iron 0.410-1482
Tin 0.060- 103.4
Phosphorus 0.020- 144.0
Total suspended solids 0.100-9970
The results of analysis of the specific constituents of raw waste streams,
2.10
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from 50 metal finishing establishment^ are presented in Table 2.6 through
Table 2.7.
Table 2.6 Composition of Kaw Waste- Streams from
Anodizjnp. (in ing/I.)
Chromium, total 0.268- 79.20
Chromium, hexavalont 0.005- 5.000
Cyanide, total 0.005- 73.00
Cyanide, amenable tc chlorlnation 0.004- 67.56
Phosphorus 0.176- 33.00
Total suspended solids 36.09 -924.0
Table 2.7 Composition of Raw Waste Streams from
Co.itin^s (in mg/L)
Chromium, tota : 0.190- 79.20
Chromium, hexav.ilent 0.005- 5.000
Zinc 0.138- 200.0
Cyanide, total 0.005- 126.0
Cyanide, amenable to chlorination 0.004- 67.56
Iron 0.410- 168.0
Tin 0.102- 6.569
Phosphorus 0.060- 53.30
suspended solids 19.12 -5275
Table 2.8 presents a summary of a survey showing that a substantial
number of evaporation, ion exchange, and reverse osmosis units arc currently
used in a variety of recovery applications.
Table 2.8 Current Application of Leading Recovery
Techniques for Klectroplatin;; and Metal
Finishing
Application
Chromium plating
Nickel plating
Copper plating
Zinc plating
Cadmium plating
Silver/gold plating
Brass/bronze plating
Other cyanide plating
Mixed plating wastes
Chromic acid etching
Other
Unit
Evaporation
158
63
19
7
68
13
10
6
6
16
s in Operation
Ion
Exchange
50
38
—
—
—
20
—
—
11
—
2
Reverse
Osmosis
106
3
3
—
6
1
2,11
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2. Iron and Steel
Tin? production of Hteel involves three basic processes:
1. Coal is converted to coke
2. Coke is combined with iron bearing material and limestone and
reduced in a blast furnace to form molten iron and
3. Iron is then purified into steel in an open hearth, basic
oxygen or electric arc furnace.
Two of the processes involved in this operation that can be documented
to provide product recovery are as follows.
1. Cokemaking
Cokemaking operations include by-product recovery and beehive facilities.
Nearly all the metallurgical coke produced in the United States is made in by-
product recovery coke ovens.
The by-product recovery process not only produces high quality coke for
use as blast furnace or foundry fuels and carbon sources, but also provides a
means of recovering valuable byproducts of the distillation reactions. The
volatiles are recovered from the gas stream and processed in a variety of ways
to produce tars, light oils, phenolates, ammonium compounds, and napthalenc
(Table 2.9).
Table 2.9 Materials Recovered in By-Producl Cokemaking Operations
Material Extent of Recovery Use
Crude coal tar All plants Resale and/or
further processing
Crude light oils Most plants Resale and/or
reuse
Ammonia and Most plants Recirculation
ammonium compounds
Phenol, phenolates, Most plants steam strip-free ammonia Reuse on-site
carbolates from excess ammonia
Half of these plants recovery fixed
ammonia
Sulphur and sulphur About 1/3 of the plants desulphurize Reuse on-site
compounds
Napthalene About 70% of the plants No information
2.12
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2. Acid Pickling
During the forming £,nd finishing operations, the steel is exposed to the
atmosphere causing an oxide scale to form on its surface. Before further
processing, this scale must be removed as it interferes with the application
of protective coatings to the steel and for cold rolling. An acid pickling
solution is used to remove the scale. Regardless of the type of acid used,
sulfuric, hydrochloric or a combination of these two, the spent pickle liquors
(SPL) are highly contaminated. Approximately 1.4 hlllioi. gallons of spent
pickle liquor is generated annually: 500 million gallons of spent sulfuric
acid; 800 million gallons of spent hydrochloric acid; and 74 million gallons
of combination pickling acids.
Following is an explanation of sulfuric and hydrochloric recovery and
regeneration technologies.
Sulfuric Acid Recovery - The most common treatment method for
recovering valuable products from spent sulfuric acid is acid
recovery by removing ferrous sulfate through crystallisation.
Spent pickle liquor, which is high in iron content, is pumped
into a crystallizer, where the iron is precipitated (under
refrigeration or vacuum) as ferrous sulfate heptahydrate crys-
tals. As the crystals are formed, water is removed and the
free acid content of the solution increases to a level where
it is reusable in the pickling operation. The crystals are
separated from the solution, and the recovered acid is pumped back
to the pickling tank. The by-product ferrous sulfate heptahy-
drate is commercially marketable. The crystals are dried,
bagged, and marketed, or sold in bulk quantities. Ferrous
sulfate, commonly referred to as "copperas," is used in appre-
ciable quantities in numerous industries, including the manu-
facture of inks, dyes, paints, and fertilizers. It is also
used as a coagulant in water and wastewatcr treatment.
Hydrochloric Acid Regeneration - The only commercially proven
technology to regenerate spent hydrochloric acid is through
thermal decomposition. The spent pickle liquor contains free
hydrochloric acid, ferrous chloride, and water. The liquor
is heated to remove some of the water through evaporation and
to concentrate the solution. The concentrated solution is
2.13
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then further heated to 925° to 1050°C (1700° to 1920°F). At
this temperature, water is completely evaporated and the ferrous
chloride decompose:; into iron oxide (ferric oxide, Fe,;0^)
and hydrogen chloride (KC1) gas. The iron oxide ir> separated
and removed froin the system. The hydrogen chloride gas is
reabsorb''d in water (sometimes rinseuater or scrubber water
is used), to produce hydrochloric acid solution (generally
from IbZ to 21% 11C1) which is reused in the pick]ing operation,
There are several types of these "roaster" processes in opera-
tion.
2.14
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References
MRI Project No. RA-219-N,. "Alternatives to Conventional Pollution Control",
1980.
Kremer, F., Broomfield, B., "Recovery of Materials and Energy. From
Industrial Wastewaters." Argonne National Laboratory, December 1981.
2.15
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CHAl'THK 3
SECTION 1
RESOURCE RECOVERY FROM HAZARDOUS WASTE
3.1 INTRODUCTION
The generation of increasing amounts of hazardous and toxic wastes
associated with the nation's rapid industrial expansion represents a problem
of increasing public concern. The Environmental Protection Agency, has
recently presented statistics indicating that 10-15% of the 344 million
metric tons of wet industrial wastes that are produced each year can be
classified as being hazardous (US EPA, 1974).
Hazardous wastes have been variously defined. The Resource Conservation
and Recovery Act of 1976 (RCRA) defines a hazardous waste in Section 1004(5)
as:
A solid waste, or combination of solid wastes, which because of
its quantity, conc.entiation, or physical, chemical or infectious
characteristics may -
- Cause or significantly contribute to an increase in mortality
or an increase in serious irreversible, or incapacitating
reversible illness, or
pose a substantial present or potential hazard to human
health or the environment when improperly treated, stored,
transported, or disposed of, or otherwise managed.
More recently EPA has attempted to identify hazardous wastes in terms
of certain characteristics as (US EPA, 1974):
ignitability
corrosivity
. reactivity
toxicity
3.1
-------
Resource recovery is attractive both lor economic and environmental reasons.
Recovery of waste energy or material value is becoming an increasingly viable
option, as ultimate disposal options become more strictly regulated and
expensive. The market for recovery has beji^n to develop an Industry, includ-
ing centralized coronercial processing and recovery facilities, and industrial
waste exchanges.
Resource recovery typically involves recycle and reuse, either with or
without pretreatment before reuse. Each increment of hazardous waste which
is recycled has value, plus represents an increment of material not requiring
detoxification and/or ultimate disposal.
The State of California has recently reported five alternatives to
landfill which are to be encouraged by regulatory and other efforts. In
order of preference these are: source reduction by changing industrial
processes to generate less waste; waste recycling and resource recovery;
physical, chemical, or biologicai treatment that renders the waste innocuous;
high-temperature incineration for many organic compounds; and solidification
or stabilization methods that chemically fix or encapsulate the wastes so
that they are less mobile in the environment. Sines 1977, the State of
California has had an active program to investigate the feasibility of
recycling hazardous wastes and to develop techniques to encourage such reuse
in California. This program includes research and development, and technical
liaison through a combined clearinghouse-consultation approach with industry,
and has resulted in a successful and growing trend of recycle and recovery.
On the basis of experience to date, the State has identified five broad
recycling categories of hazardous wastes;
Type I Unused commercial chemicals in packages.
3.2
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Typo II Process wastes that .ire economically and technologically
feasible for recycle without prior treatment.
Typo III Process wastes that are ejotso;r.ically and technologically
feasible to recycle if pretruated.
Type IV Process wastes that are not presently economically and
technologically feasible to recycle.
Type V Wastes that are undesirable to recycle.
Type IV wastes may shift to the Type II or III category as the experience
and data base for recycle expands. Type V wastes include those extremely
hazaidous substances (carcinogens, pesticides) that must be destroyed due to
bans or restrictions on their use.
3,2 Resource Recovery
Before specific processes and alternatives for resource recovery are
discussed, it is necessary to describe broad strategies for the recovery of
economic value from hazardous waste processing. In general, there exist
four broad paths whereby recovery of some value from waste may occur:
Direct recycle for primary (generator) use
Use by a second industry as a raw material
Energy recovery
Utilization in pollution control systems
A given hazardous waste stream may be a potential candidate for recovery by
more than one of the above routes; however consideration of the benefits to
be derived will provide guidance in determining needed pretreatment methods
to be used.
Direct Recycle. One route for reuse of a hazardous waste is the pro-
cessing of the waste stream to recover materials of value to the industry
which generated the waste. For larger generators, strong economic incentives
3.3
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to implement direct recycle options oxist. However at smaller generators, the
cost of recovery nay negate any value to be recovered; hore the possibility
exists for collection and recovery by a contract processor.
Some instances of direct recycle, to be elaborated upon belou, include
chromic acid recovery from spent plating bath solutions, and organic solvent
recovery from degreanlng operations.
Recycle to a Second Industry. By definition, the wastes disposed of by
an industry have no intrinsic value to that industry so, that in many cases,
direct recycle is not a viable option. However, the waste fron a given
industry may contain material of value to another Industry, and may represent
a competitive source of supply of that material, cither with or without
intermediate purification and/or enrichment.
Example possibilities for secondary recovery include solvent recovery,
recovery of phenols from coking wastes, sulfur recovery from stack gas
cleanup, and tretal and/or acid recovery from various pickle liquors. Indus-
trial waste exchanges perform a secondary recovery function, by accepting
wastes from one site, and providing it as a process chemical to another.
Energy Recovery. Many hazardous wastes, particularly those containing
organic matter, have ?"fficient energy value to enable recovery of energy to
be economically viable. The most common implementation of this strategy is
the use of spent solvents or waste oils for steam generation. An additional,
and attractive, option would appear to be the use of waste chlorinated
solvents as alternate fuel r lurces in cement manufacture. Energy recovery
may occur at the site of the generator, or at a secondary site.
Recovery for Pollution Control. In some cases, the value of a given
waste straam may be realized by using the waste stream in the control of
3.4
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other pollutants, in place of more expensive nlttrri.it ivo Ireatr <_rit reagents.
The cose coaiaon UKP of this strategy is tht: neutralisation of waste by nix in,.,
an acidic and an jlkalinc waste stream. Another promising strategy is the use
of waste pickle liquor for hydrogen sulfide or phosphorous control in waste-
water treatnent plants.
3.3 UMT PROCESSES USE!) IN RESOURCE RECOVERY
The treatment which a specific hazardous waste receives prior to resource
recovery may consist of a number of discrete unit processes, which depend upon
the nature of the material, the nature of the desired end-product and the type
and extent of contamination. Many other factors will influence the selection
of processes that are chosen, such as economics, geographical considerations,
and Federal, State and local environmental regulations. Specific examples
will be discussed in a later section when individual wastes are considered.
»
A brief summary of each process, and)types of applications that nay be
important in hazardous waste processing is given in Table 2.
3.4 EXAMPLE RESOURCE RECOVERY OPTIONS
Resource recovery options exist for many of the types of hazardous
wastes, ami will be discussed in this section.
Recovery from Acidic Wastes. As indicated in Chapter 1, it is estimated
that about 35% of all liquid wastes (contain acids. In the case of acid
recovery from relatively uncontaminated solutions, the ptu ication and
recovery of the acid is technically feasible. However, the economics strongly
depend on the acid concentration, and local factors, auch as transportation
costs.
In the case of nitric acid wastes, recovery may be effected by steam
distillation. The recovered product, after condensation, consists of a
3.5
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,aixture of 68>. acid and 32/J water, which is the constant boiling point compo-
sition. This product may then find numerous industrial uses. The waste from
the recovery operations, consisting of still bottoms, would be neutralized and,
where necessary, given further treatment, and any residue disposed of in a
secure landfill (Ottinger, et_ jil., undated).
In the case of wastes containing sulfuric acid, recovery can be effected
if the following requirements are met:
The recovery operation is near an existing sulfuric acid plane.
Waste contains more than 70% acid.
Waste volume is greater than 50 tons/day.
Organic impurities are low.
Inorganic impurities are low.
The recovery process involves the use of heat to decompose the acid into
sulfur dioxide, which evolves as a gas. The gas stream is then collected and
piped to the sulfuric acid manufacturing operation for use as a raw material
(Ottinger, et_ a\_., undated).
Acid Solutions Containing Metals. Acidic solutions containing metals
arise from metal finishing operations; from electroplating operations, both
as spent plating solutions and as rinsewaters; from the steel industrial
processes. There may be a potential for recovery of either or both the acid
and the metal contained in the waste.
In the case of waste pickle liquor, it is possible to use the waste
directly in pollution control. The ferrous iron salts that may constitute
as much as 15% of the waste, have been useful for the removal of phosphorus
from wastewater effluents by precipitation (Ottinger, et a_l., undated).
Recovery of metals from other wastewaters may be effected by various
precipitation or ion exchange processes. These have generally been designed
or discussed on a case-by-case basis, with the principal exception of chromium
3.6
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recovery. (Ueber, 1972) has outlined a three-bed process for the treatment
of chrome plating wastes, involving recovery of treated water strong (4-6%)
chromic acid solution, and separated metal sulfates in a regenerant v/aste
stream.
In the case of most other metals, the initial step in recovery from an
acidic waste strea-n would appear to involve neutralization and precipitation.
The resulting sludge can then, in some cases, be treated for metal recovery.
One process proposed involves the leaching of these sludges with sulfuric
acid, and filtration, to remove solid matter, such as calcium sulfate. The
filtrate may then be neutralized to pH 3, with an alkali, to precipitate
iron hydroxide for recovery. Remaining filtrates can be electrolysed for
recovery of metallic nickel and copper. The supernate from the electrolysis
operation can then be neutralized with lime to a pH of 9, and cadmium,
chromium and zinc recovered from the precipitate. One economic analysis of
this process configuration indicated that, for a plant treating 50 tons/day
of netal sludgep a net income, exclusive of costs associated with ultimate
disposal of residuals, of $572/day was possible (Battelle Memorial Institute,
1974).
In certain cases reductive precipitation of metals from waste streams
may be practicable. In the case of chromium, reduction of hexavalent chromium
to trivalcnt chromium, followed by alkaline precipitation produces a sludge
containing chromium hydroxide. It has been proposed that this sludge may be
treated with sulfuric acid, for the recovery of chromium sulfate, and subse-
quent reuse in the leather tanning industry (Ottinger, et_a]L., 1973). In
view of the geographic concentration of leather tanning in New York, and the
proposal for a central treatment facility for this industry (lannotti, et
3.7
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al., 1979), possible implementation of such a chrome recovery step may be
appropriate.
For the recovery ot" nickel, copper, and silver from waste-waters, reduc-
tive precipitation has also been proposed. After silver solutions are
contacted with zinc dust, metallic silver can be recovered (Battelle Memorial
Institute, 1974). Treatment of wastes containing nickel or copper with iron
filings at a pH in excess of 3.5 may also result in the recovery of metallic
nickel or copper (Battelle Memorial Institute, 1974).
Acid Solutions Containing Organics
Many wastes fall in this category, ranging from minuscule flows to vary
large flows and varying from lov; concentrations of both acids and organics,
to very high concentrations of either or both components. The organics nay
be present either in emulsified f ;rra or in dissolved form.
Resource recovery may be directed in one of two directions for waste
streams containing substantial quantities of components.
neutralization of acid and recovery of organics
removal of trace organics and recovery of acids
Neutralization of acid wastes containing emulsified organics often
causes the emulsion to break and allow the separation of a suhsttmtial
fraction of the organic material which can be removed by skitnraing or decanta-
tion. If the quantity of organics warrants recovery, it raay be fractionated
and purified by distillation. Otherwise the organic layer can be removed
and incinerated. Any residual dissolved organics raay be removed by one of
several techniques such as adsorption, flotation or extraction, or one of
the biological treatment methods. Recovery of grease and oil from acid
wastes is often feasible, e.g. acid waste streams from refineries or from
electroplating, or metal finishing operations (Hall, 1978; Tabakin, 1978;
3.8
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Luthcy, 1578; Steiner, 1978; Humcnick, 197H; Levin, 1981).
If the quantity of organics in acid wastes Is nmall they may be removed
by techniques such as adsorption, flotation or extraction. The remaining
acid, If in attractive quantity, can be removed and recovered or possibly
reused by the techniques discussed earlier In this section. It may be noted
that increased attention has recently been given to the recovery of acids
from pickle liquor (U'adhawan, 1978).
Acid Sludges
Acid sludges cone from a wide variety of industrial processes and vary
widely in quantity and composition. They often are highly viscous which
makes further processing quite difficult. It therefore, is unlikely that
any great potential exists for recovery except iri special situations which
must be evaluated on a case to case basis.
An exception to the above statement is the case of acid sludges fron
electroplating operations. These sludges may contain metals together with
high concentrations of acids which makeo the waste hazardous. Recovery of
the raetals may be accomplished by extraction with suitable solvents or acids
and subsequent recovery of the metals by ion exchange or neutralization,
precipitations and filtration. Thus recovery, treatment and disposal can be
incorporated in the same process (Gurnham, 1965; Nemerow, 1978; Leonard,
1971).
Acid Gases
The potential for recovery or reuse Is small except in some special
cases. For instance flue gas is sometimes used to neutralize alkaline
liquid wastes, utilizing the acidic components of SO and CO. (Kemerow, 1978;
Steele, 1954; Cana, 1959; Ficco, 1960). Seme instances of HC1 recovery by
3.9
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absorption and concentration have also been reported (Nemerow, 1978;
Besselievre, 1969; Curnham, 1955).
Resource Recovery fron Alkaline Wastes
Alkaline wastes may be generated in a variety of industries, including
electroplating and textiles. Some of these wastes may contain cyanides and
metals, as in electroplating; other wastes may contain high concentrations
of organics and/or solids, as in textile manufacture. Resource recovery
strategies may include recovery of the alkali itself, or recovery of the
other materials contained therein. In addition, the possible use of any
alkaline material as a scrubber feed should be mentioned, for possible use
in the removal of acid gases from incinerator stack gases.
Alkaline Solutions Containing Metals
The major class of wastes of this group is that arising from electro-
plating wastes containing metal cyanides. This type of waste is widespread
in masiy major industrial centers, A potential exists for resource recovery
and various recovery strategies have been described.
Three possibilities for recovery have been described. A simple evapora-
tive distillation to recover water, and concentrated metal cyanide solution
i
can be carried out to permit reuse at the point of generation. (Ottinger,
et_ ai., 1973). A second strategy for tnetal recovery alone involves the
addition of metallic iron to the? waste, to allow the precipitation of
elemental copper and nickel from the solution (Ottinger, ejt al., 1973). The
residual will contain cyanide, which must be further processor, prior to
ultimate disposal.
Both the nietal and the cyanide may be recovered if an : .
-------
exchanger and a cation exchanger, and the waste Is passed through the two
columns in series. In the cation exchanger, regeneration yields a metal
solution, typically metal chloride, i£ brine is used as a regenerant. In
the anion exchanger, use of either caustic or brine as a regenerant will
allow recovery of sodium cyanide. The resulting metal chloride stream and
sodium cyanide stream may then be used in the plating process, or sold for a
secondary use (Ottinger, e± ajk, 1973; Booz Allen Research Inc., 1973).
Alkaline Solutions Containing Organics
If the organic material present in these wastes is at a sufficiently
high concentration, and is of a nature where recovery is desirable, then
alkaline solutions containing organics may be treated for recovery of the
organic fraction according to procedures described in a later section. For
several waste streams, however, the nature of the organic contaminant, or
its concentration, are such that organic recovery is either not practicable
or economic. In these coses, recovery of tb.2 alkali might be investigated.
As an example: of this possibility, wastes front textile processing rcay
Consist of a strong caustic solution, routinely contaminated with hemiceilu-
lose. In a full scale installation, use of dialysis for the recovery of a
9-10% caustic solution, free of organic impurities, has been found feasible,
and has resulted in a recovery of 200 tons/yr of sodium hydroxide (lannotti,
et_ jvl., 1979). It would be anticipated that this technique can be applied
to strong alkaline solutions containing organic contaminants, provided that
other inorganic contaminants and suspended solids concentrations were rela-
tively low.
Alkaline Sludges
Alkaline sludges may arise in a number of industrial processes. The
3.1).
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most corr.raori type of alkaline sludges lor which resource recovery processes
have been proposed is Che sludge resulting from chloral k;il 1 manufacture.
These wastes nay contain lead, where the diaphragm cell process is used, and
mercury from electrode contamination and brine impurities.
It has been proposed that lead recovery froai waste sludges of the
diaphragm cell process could be carried out using smelting. The sludge to
be treated is dewatered, using coagulants, and filtration, no 2f% solids.
The dewatered sludge can then be blended with lime, silica, and ccke, and
smelted in a reducing atmosphere at 1000-1040°C for lead recovery in the
ash. Using this process, air pollution controls on the smelter would be
necessary, and the filtrate from the devatering operation could be sent to
the main vater treatment plant (Shaver, jsf: jal, 1975). The estimated cost of
this process was $0.81/metric ton of chlorine produced.
Two mercury recovery processes for chloralkali sludges have been
proposed, and are currently in use in industrial applications. Georgia-
Pacific in Eellinghan, WA has been reported to use a dewatering process,
followed by roasting to recover mercury. The n.ercury vapor is recovered
from the combustion gases by condensation and demisting. The data from the
full scale installation permits a cost estimation, including recovery of
mercury, of $2.50-2.90/metric ton of chlorine produced (Shaver et al.,
1975).
Mercury recovery from a similar waste by a non-thermal process is prac-
ticed at the BASF Wyandotte plant, Fort Edwards, WI. The brine purification
muds are acidified to pH 2 with waste concentrated sulfuric acid, and calcium
carbonate is alloweu to precipitate. The mixture is then treated with
sodium hypochlorite at pH 6-7 to dissolve the mercury from the sludge.
3.12
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Vacuum filtration to remove the n-nui inin;; low-mercury solids for disposal,
and collection of the mercury-laden filtrate is then performed. The filtrate
is then combined with other ciercury laden wastes, ond treated with sodiuro
bisulfite, sulfuric acid and sodium hydrosulfide for about 16 hours to preci-
pitate mercuric sulfide. The mercuric sulfide can be recovered as a filter
cake by leaf filtration. The effluent can then be discharged, after batch-
wise monitoring for mercury levels. The mercuric sulfide may be used off-
site, or may be dissolved in sodiua hypochlorite and the solution recycled
to the main plant brine circuit. Operating data from full scale installation
indicate a net cost of $6.90/metric ton of chlorine produced (Shaver et al. ,
1975).
Resource Recovery from Other Inorganic Wastes
Various waste streams may be generated that contain hazardous inorganic
materials such as salt solutions, solid salts, metals and non-Eetals. A wide
range of materials and concentrations are encountered, and the possibility
of recovery or reuse must be evaluated for individual situations.
Salt Solutions
There does not appear' to be a high potential for recovery from
wastes of this type. Some process solutions may contain hazardous
salts in sufficient concentrations to warrant recovery, such as fluo-
rides from smelting operations (Gurnham, 1965). Various concentration
techniques such as evaporation may be necessary as pretreatment and
they are usually expensive because of investment costs and high heat
costs. Reuse of waste salt solutions can sometimes be practiced,
either within the same process from which waste originated or in neigh-
boring processes or other industries.
3.13
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Solid Salts
Various metal-finishing industries discharge batches of salts used
as noltcn salt baths for heat-treating. These baths often contain
cyanides, fluorides, and other salts with toxic properties. Recovery
from these mixtures is possible by dissolving, filtering and recrystal-
lizing the salts. Such processing is, however, unlikely to be cost
effective (Ottingcr et_ a±., 1973; Shaver £t_ al_., 1975; Genser et. al.,
1977).
Metals
The electrolytic refining of copper results in the generation of
an anode mud which contains hazardous materials such as arsenic, anti-
mony, nickel, selenium and tellurium. The concentrations of thcsi.'
materials may be high enough to justify extraction and recovery of
these materials by ion exchange or electrolysis (Gumham, 1965).
Some metal refineries and other industries generate metallic dusts
which are usually water scrubbed for removal of entrained solids.
Recovery from the scrubber water by filtration is practiced (Leonard ejt
al., 1977).
Wastes discharged frcra some chlorine-alkali electrolytic -.ells
often contain substantial amounts of mercury. The mercury can and
should be recovered by controlled incineration or retorting followed by
condensation of the mercury combined with vapor cleanup with mist
eliminators, adsorption and activated carbon or scrubbing with hypo-
chlorite solutions (Ottinger jst al., 1973; Shaver et_ al., 1975; Booz
Allen Research Institute, 1973).
Lead is frequently recovered from storage batteries and other
3.14
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waste materials. Carefully controlled smelting or burning techniques
have been used to recover the lead. The value of lead makes its re-
covery attractive (Curn'mm, 1965; Battelle Memorial Institute, 1974).
Non-Heta_ls
A potential exists for the recovery and reuse of sulfur from a
number of ccTrr.ion hazardous waste streams. Many processes found in such
industries as the coke and steel industry, tanneries and various
chemical industries generate toxic sulfur compounds. These cisterials
often appear in alkaline scrubbing wastes or other wr.ste solutions.
The sulfur compounds can often be concentrated by steara stripping,
converted to hydrogen sulfide and then reduced to elemental sulfur by
the Claus Process or one of its modification (Ottinger et a_l., 1973).
Resource Recovery from Concentrated Organic Liquids
The potential for resource recovery from concentrated organic liquid
wastes arises from the economic, material and energy values resulting from
the presence of certain specific organic materials, such as solvents, within
the waste stream. For lightly contaminated material, resource recovery is
relatively easier than for heavily contaminated waute. However, in general,
all strategies embody some degree of purification, which results in both
recovery of a more usable product, and partial detoxification and volume
reduction of 'the residual waste.
Lightly Contaminated Wastes
In a wide variety of industries, recovery of solvents from lightly
contaminated wastes is feasible, and is currently practiced. It has been
estimated that some pharmaceutical companies recycle over 99% of the hazard-
ous solvents which they use (Booz Allen Research Institute, 1973). In the
3.15
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electronic components industry, surveys indicate that over half of both the
halogenated and non-halogenated solvents arc1 segregated for reclamation
(Peters et_ al^. , 1977). A wide variety of solvents and other organics may
thus be reused, including the halogeruited methanes and ethanes (FEA, 19/6).
Techniques used for solvent and organic recovery vary with the nature of
the waste and the product c'esired. In some cases, relatively clean solvents
may be wasted, and simple repacking for use by other commercial users is
adequate (Peters je_t_ jrl., 1977). More commonly, distillation end recondensa-
tion are used to recover desired solvents (Peters et^ al., 1977; FEA, 197u).
Several commercial reclamation services employ extensive distillation or
fractional distillation processes for solvent recovery.
A detailed process design lias been published, involving multiple distil-
lation and condensation steps, which is claimed suitable for separation and
recovery of the following organic solvents: raethylene chloride, chloroform,
methyl chloride, chloroform, ethylene dichloride, trichloroeehylene, per-
chloroethylene, and o-dichlcrobenzene (Battc-lle Memorial Institute, 1974).
It should be etsphasized that in any recovery strategy such as this, a resi-
dual will always be present, typically as a still bottom, and roust receive
adequate consideration for proper disposal.
Heavily Contaminated Wastes
In the case of heavily contaminated wastes, recovery of organic materials
may be effected in a similar manner to that for lightly contaminated
materials, especially in cases where there is a significant difference in
boiling point between the desired material and the contaminants. While these
potentials need to be evaluated on a case-by-case basis, several examples of
promising recovery techniques have been reported.
3.16
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In the wool industry, scouring and degreasing operatior.j may result in
a solvent heavily contaminated with lanolin and other greases. The solvent
may be distilled and recycled within the plant; the still bottoms, consisting
primarily of lanolin and grease, may also be recovered, if a satisfactory
market is available (Booz Allen Research Inc., 1973).
In the petroleum industry, wastes from process condensate or steam
stripper condensate or bottoms may be heavily contaminated with phenol. A
proprietary solvent extraction process, the PHENEX process, has been proposed
for recovery of phenol and removal of this material from the liquid stream
(Booz Allen Research Inc., 1973).
In a number of industries, heavy ends or still bottoms are produced
from distillation or other processes. Typically, in the organic chemical
industries, liquids or semisolid wastes may result from the manufacturing
process. Again, resource recovery from wastes of this nature may require a
case-by-case analysis. However, two case studies from the literature are
given to illustrate potential for resource recovery.
In the manufacture of chloromethane solvents; a waste stream is
produced consisting of ;>exachlorobenzene, hexachlorobutadiene, and miscella-
neous materials. An initial distillation of this waste yields a distillate
which may be chlorinated at high temperature and pressure in a nickel tube
to yield carbon tetrachloride. After quenching, and partial cooling and de-
pressurization, the high boiling compounds may be distilled off and recycled
back to th'_- chlorine contactor. The remaining material may be separated
into cnlorine and carbon tetrachloride by distillation. The carbon tetra-
chloride may be further purified and marketed with the production from the
main plant. Economics of this process indicate favorable costs, of about
3.17
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1-2% of the total product value (Genser et^ a^., 1977).
In the manufacture of perchloroethylene, a waste stream Is produced
which consists primarily of hexachlorobutadicne. liy stripping the volatile
material from this waste, recycling this to the main plant, and distillation
of the remainder, hexachlorobutadiene can be produced. Including costs for
land disposal of the still bottoms from the recovery operation, economic
analysis indicates the potential for a net profit from the treatment/recovery
operation (Genser ef_ al., 1977).
Resource Recovery from Dilute Aqueous Solutions of Organic;?
There does not appear to be any significant potential In the near term
for resource recovery from dilute aqueous solutions containing organic matter.
The only possible exception to this statement may be in the case of highly
specialized waste streams, such as those from the pharmaceutical industry,
which might contain low concentrations of relatively valuable material. The
raajor basis for this pessimism lies in the relatively high costs of probable
separation processes which might be used to purify and concentrate the organic
contaminants into a usable product.
The only possible recovery strategy for this group of wastes currently
forseeable is the possible recovery of energy from this material when acti-
vated carbon is used in rerooval. In this case, during the thermal regenera-
tion of carbon the process might be operated to provide a beneficial use of
waste heat. It would not appear, however, from a cursory analysis, that this
option will permit a net production, of energy in the GAG process.
Resource Recovery from Organic Solids
Although the major aims of hazardous waste disposal of organic solids
are detoxification and volume reduction, opportunities exist for resource
3.18
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recovery. The general strategies used are energy recovery, direct recycling
as a raw material in another industry or use of a pyrolytic system to generate
liquid or gaseous fuels. Energy recovery from thermal processing is covered
in a later section.
Contaminated organic solids (or liquids) which cannot be recycled must
ultimately be diposed of by incineration. In some cases, recovery of the
contaminate will result in a usable product. For example, hydrogen chloride
is produced during incineration of chlorinated hydrocarbons. To meet air
pollution regulations, this gas must be collected. Since hydrogen chloride
or hydrochloric acid has economic value, its presence then becomes a credit
rather than a liability (Novak, 1970; Ross, 1977; Santoleri, 1973).
Salts and Pure Organic Compounds
Although the volume of waste in this category is, in many locations,
very small, salts and pure organic compounds are the best candidates for
if
direct recycling (Tabakin c_t al_., 1978). Wastes from one industry can
sometimes be used directly as a raw material for another industry. This
exchange can only take place when a mechanism exists for easy transfer.
Hazardous waste clearinghouses provide this avenue for exchange (US EPA,
1976; Terry £t a_l., 1976).
Tars and Residues
Tars and residues generally have little value for resource recovery
other than their heat content. Energy recovery after thermal processing
is possible if the heat content of the waste is high enough. However,
with increased energy costs the fuel quality of residues has been
steadily decreasing (Novak, 1970).
Sludges
Since uost hazardous organic sludges commonly will require
3.19
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incineration, several possible methods of resource recovery might be
feasible other than recovery.
Recovery of inorganic contaminants after incineration from the
scrubber water or ash is possible. Metal oxides have some economic
value, and can be recovered bv extraction and ion exchange. These
compounds can be reprocessed to recover the metals. Recovery of halogens
from the scrubber water is another possible direction. For example,
brominated tars and sludges, when incinerated, release free bromine.
Recovery of the relatively valuable bromine, rather than its complete
disposal, seems practicable (Kivak, 1970; Sebastian» 1975; Folks £t. al. ,
1975; Santoleri, 1973; Ross, 1977; Hitchcock, 1979).
Resource Recovery from Organic Gases and Vapors
Organic gases and vapors will usually be incinerated or recycled at the
point of production. Recycling is accomplished by solvent stripping, extrac-
tion or condensation. Tanked gases have the possibility of direct recycling
as a raw material for another industry. Unwanted gases and organic vapors
produced during disposal should be incinerated and can be used for energy
recovery.
3.5 Energy Recovery
The recovery of energy and/or besting value from certain organic hazard-
ous wastes is deserving of special consideration. In general, few incinera-
tion systems for toxic waste decomposition have been designed to recover
energy since auxiliary fuel is almost always needed to ensure complete com-
bustion with minimization of undesirable atmospheric emissions. However,
knowledge of detailed feed composition and careful blending of wastes fed to
an incinerator will reduce the auxiliary fuel needs, and thus reduce direct
3.20
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energy costs associated with incimration.
There are two basic manners in which energy recovery may be effected in
thermal processing: heat recovery, and recovery of fuel value. Recovered
heat may be used to preheat combustion air, or in steam generation for heat
or power production. Heat exchangers are generally tubular, plate, or
regenerative, and used for heat transfer between the exit, gases of a combus-
tion process and a working fluid. If air is the working fluid across a heat
exchanger, it can be used as input to the combustion chamber to minimize fuel
use. If the working fluid is water, the resulting steam or hot water may be
sold or used in plant processes.
The second major type of energy recovery is utilization of the fuel
value directly. Under pyrolytic conditions, a combustible liquid or gas may
be produced from hazardous waste, which can be sold or used elsewhere (llovak,
1970; Ross, 1977; Boucher et_ al., 1977; Folks et_ al., 1975; Sebastian, 1975;
Hitchcock, 1979). An interesting opportunity for conservation of the fuel
value of hazardous waste is the utilization of these materials as feed for
rotary kilns in cement manufacture. Test burns of chlorinated hazardous
wastes at the St. Lawrence Cement facility in Ontario showed a 99.98 percent
destruction of PCB's and a 99.99 percent destruction of chlorinated organics
(US EPA, 1975). In this process, halogen gases are scrubbed into the cement
product, and the fuel value of the hazardous waste directly reduces the need
/or fossil fuel inputs. A typical cement plant may reqt ire 10 BTU of fuel
per day, and initial indications suggest that substitution of up to 15
percent of this fuel value with chemical waste is possible (Alpha Portland
Industries, personal communication). Certain industrials produce solvent
laden air streams, which must normally be treated to control air emissions.
One alternative to treatment and production of a solvent waste for disposal
3.21
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is to directly use the solvent laden air as the air feed to c. boiler. The
fuel value of the solvent is then recovered in the boiler.
In energy recovery from hazardous wastes, as in incineration of chemical
wastes in general, the issues of materials deterioration regain relatively
poorly understood. Operating problems such as corrosion, erosion, plugging,
fouling, and refractory decomposition can decrease useful life of components.
In addition, any utilization of energy in outside industries necessitates the
production of a consistent amount of steam and/or fuel, and thus a relatively
constant throughput of hazardous waste, both in terms of quality and quantity,
must be maintained.
3.6 FACILITATION OF RECOVERY
Industrial materials are perceived as special or hazardous wastes requir-
ing disposal when, in the judgment of the waste generator, there is insuffi-
cient economic value associated with the waste to warrant alternative modes of
utilization. This judgment may be predicated upon institutional regulations,
or upon a lack of awareness of a potential secondary industrial market for
the material. Facilitation of recovery thus must consider both institutional
options and strategies to encourage alternatives to ultimate disposal, and
methods to identify secondary recovery and reuse markets. This latter aspect
is usually addressed through waste exchangers and information clearinghouses.
Institutional Options. The National Conference of State Legislatures
has recently completed a survey and analysis of state policy options to
encourage alternatives to land disposal of hazardous wastes. This analysis
identified several state options to encourage the use, reuse, reclamation,
and recycling of hazardous waste. The states can encourage such alternatives
to land disposal by providing finane'.al, legal and institutional incentives
and disincentives.
3.22
-------
A variety of financial strategies have been described lor encouraging
alternative methods for management of hazardous waste. They include the use
of fee structures, tax incentives and bonds. Fees can be structured to
discourage undesirable disposal options such as land disposal, by making them
higher for those generators who do not utilize use and reuse methods. They
can encourage alternatives by setting lower fees for.permits and licenses
required of facilities that treat or recover hazardous waste. Tax incentives
offer a positive inducement for business and industry to adept alternative
waste management methods. They include property and equipment tax exemptions,
corporate income tax exemptions, accelerated depreciation schedules and
sales, and use and excise tax exemptions for facilities which treat and
recycle hazardous waste. Industrial revenue bonds may also be authorized to
finance resource recovery facilities.
Illinois, for example, currently levies a uniform fee on all owners and
operators of hazardous waste sites. Some other states structure fees to be
higher for, or to be only levied on, those generators who do not utilise
reuse and reduction methods.
Kansas authorises its Department of Health and Environment, and
Tennessee its Solid Waste Control Board, to establish a schedule of fees
based on the degree of hazard and costs for treatment and disposal. In
effect, these approaches allow the state to discourage high hazard waste
disposal by scheduling higher fees for these facilities. Indiana places a
tax of $1.50/ton on hazardous waste disposal, but it appears that, this tax
does not apply to resource recovery. In Ohio, those entities that detoxify
cr incinerate hazardous waste are not required to pay the fee which supports
the state's special hazardous waste account. Such an approach places the
3.23
-------
financial burden on chose facilities which would have the greatest tendency
to call on the resources of the fund.
Recent Kentucky legislation authorizes the Department for Natural
Resources and Environmental Projection to collect a tax. The annual hazardous
waste management assessment is determined according to the quantity and
volume of hazardous waste generated by the individual. The assessment fov
on-site treatment and disposal is one-half the amount for off-site treatment
and disposal. On-site resource recovery and treatment facilities are exempt
from any assessment unless the process involves the landfilling of hazardous
waste. The legislative intent of the assessment is to reduce the amount of
waste generated, promote alternatives to landfilling and encourage onsite as
opposed to offsite management. The assessment on generators of waste destined
for long-term containment without prior treatment is significantly higher than
for generators of waste destined for treatment. This approach rewards those
generators who provide pretreattpenc of their waste. In addition, the Depart-
ment has developed a schedule of fcca for the costs of processing applications
for permits and exemptions that is lower for rccyclers of hazardous waste.
Maine's proposed three-tiered fee structure is similar to Kentucky's in that
license fees, renewal fees and taxes on generators of hazardous waste will be
lower for resource recovery activity.
Florida offers an alternative approach. Rather than raising the fees
for generators who do not treat their waste, facilities which render waste
non-hazardous are exempt from the four percent excise tax. The tax is "to be
paid by each generator of hazardous waste in the state...for the privilege of
generating hazardous waste." The tax is levied at four percent of the price
of disposing, storing, or treating hazardous waste. Moreover, the tax is
3.24
-------
levied in addition to all other taxes imposed upon or paid by the generator.
In addition to exemption treatment facilities which render the waste non-
hazardous, the law exempts onsite generation and disposal. As in Kentucky,
treatment and/or onsite facilities are encouraged. Alon;^ with money collected
from permitting fees, fines, appropriations, etc., the money collected from
the excise tax is used to support the state's Hazardous Waste Management
Trust Fund. Table 3.1 is a summary of State fees on hazardous wastes disposal.
Similar to fee structures in that they may be used to encourage alterna-
tives to land disposal, tax incentives offer a positive inducement to business
and industry to adopt alternative waste management methods. While fees may
be scheduled as a disincentive to landfilling, taxes can be structured to
reward those businesses and industries that engage in treatment or recovery
of hazardous waste.
There are several types of tax incentives that can be applied specifical-
ly to hazardous waste treatment. Tax incentives provided for solid waste
facilities or pollution control equipment may also be applied to hazardous
waste management with amendment of statutory language. The range of tax
incentives includes property tax exemptions, "breaks" on equipment taxes,
corporate income tax exemptions, and sales, use and
-------
Table 3.1 Sunvmary of Selected State Hazardous Waste Disposal
Fees (Bulanowski, et al., 1981).
State
Alabama
Florida
Illinois
Indiana
Iowa
Kansas
Kentucky-
Maine
Missouri
New Jersey
Ohio
Volume Basis
gallon
ton
see Footnote (1)
gallon
cubic yard
ton
see Footnote (2)
cubic yard
gallon (1981)
gallon (1983)
gallon (on-site)
(off-site)
see Footnote (3)
see Footnote (4)
see Footnote (5)
Fee, $
0.036
5.00
***£
0.01
2.02
1.50
Art**
0.25
0.02
0.05
0.12
0.15
****
****
ft***
(1) A percent tax on charge for disposing of waste
(2) 2 percent surcharge tax
(3) 2 percent tax on gross charges and fees
(A) 5 percent tax on gross receipts of disposal facility
(5) 4 percent tax on grosc charges
3.26
-------
bonds, only five states specifically address their use in resource recovery.
These states are North Carolina, Florida, Illinois, Mississippi, and Georgia.
In Illinois, facilities for which such funds are available include those
engaged in, "reducing, controlling or preventing pollution...(or those that)
reduce the volume or composition of hazardous waste by changing or replacing
manufacturing equipment or processes...recycle hazardous waste, or recover
resources from hazardous waste."
Legal and institutional policies available to encourage land disposal
alternatives range from legislative and regulatory incentives and disincen-
tives to the establishment of state research and development pro^r^ms. In
Illinois, a portion of the State hazardous waste disposal fee is allocated
under the enabling legislation to a research and development fund. Legal
options consist of excluding recycled and reused materials from regulatory
programs; eliminating permit requirements for resource recovery facilities or
if
on-site hazardous waste systems;! expediting and the permitting process (i.e.
fast-track permitting) for recycling facilities; restricting the burial of
certain hazardous waste when it is feasible that it be treated or recycled;
i
and lessening the liability standards for alternative management technologies.
There are jwny approaches to land disposal restrictions. Perhaps the
strongest position that can be[taken is an outright ban on land burial. New
York's Department of Environmental Conservation has announced that they are
currently writing regulations to "ban landfilling of environmentally persis-
tent and highly mobile chemical wastes..." Further, New York has denied
permits on the grounds that they failed to adequately provide for technologies
that offer alternatives to land burial. Another approach to banning land
disposal of hazardous waste is to require neutralization, detoxification,
solidification or encapsulation of the waste prior to land disposal.
3.27
-------
Effective January, 1983, the State of California will baa the land
disposal of six categories of hazardous wastes which, together, represent
about 40 percent of all hazardous wastes which otherwise would be deposited
in landfills. The banned wastes consist of polychlorinated biphenyls, pesti-
cides, toxic metals, cyanides, halogenated organlcs, and non-halogenated
volatile organics. The current volume of these wastes landfilled in
California is 500,000 tons/year. The intent of the ban is to force the-
wastes to be recycled, detoxified, or destroyed, as alternatives to land
disposal.
In Illinois a petition has been filed by a citizen's group with the
Illinois Pollution Control Board, requesting that the Board promulgate a
regulation prohibiting the disposal of the class of compounds termed "chlori-
nated solvents" In landfills, as well as the sludges and still bottoms from
the recovery of these solvents. In addition, the Illinois Environmental
Protection Act was recently amended to require the 1EPA (effective January lt
1987) to permit hazardous waste disposal to a landfill only after the waste
stream generator has demonstrated to the IEPA that,..."considering technolo-
gical feasibility and economic reasonableness, the waste cannot be reasonably
recycled for reuse, incinerated or chemically, physically or biologically
treated so as to neutralize the waste and render it non-hazardous."
To make this strategy of land disposal restrictions more workable for
the regulated community, some states such as Illinois specifically require
that it must be technically feasible and economically reasonable to require
recycling or treatment. The state statutes that require this, often autho-
rize the agency to describe in rules and regulations what is technically or
economically feasible and what wastes should be restricted from landfills.
3.28
-------
The institutional strategics designed to encourage alternatives to land
disposal include establishment of government operated v;astc exchanges, re-
search ana development programs, and state ownership of alternative technology
facilities. Waste exchanges direct material that would otherwise enter the
waste stream to a beneficial use or reuse; they lower disposal costs and
conserve raw materials and energy necessary to process virgin materials.
Research and development can advance the implementation of alternative
resource recovery t2chnologies through direct state research or technical
assistance programs. Perhaps Che most effective institutional strategy is
the establishment of state-owned facilities that provide alternative technolo-
gies; this permits the regulatory agency to set specific treatment and
recycling requirements on the hazardous wastes which will be handled by the
facility.
Waste Exch'in&cs. In resource recovery of hazardous wastes it is impor-
tant to recognize that the generator of a given stream may not necessarily
recognize the potential for recovery by an industry outside of its immediate
scope of production. The process of secondary recovery car; be facilitated by
the establishment of waste exchanges.
Waste exchanges are institutions which promote waste reuse by one of two
methods. Most waste exchanges act as information clearinghouses, by collect-
ing information on materials to be disposed and potential buyers (or recipi-
ents) of such waste. Other waste exchanges act by accepting (or purchasing)
wastes from a generator for sale to a user. In the case of a waste materials
exchange the acceptance and sale may be merely a paper transaction, as in
the case of a brokerage, rather than a physical acceptance and transfer.
3.29
-------
The earliest waste exchanges were established In Western Europe-, begin-
ning in 1972. These European organizations now typically have a 30-40 percent
success rate in exchanging materials contained in their listing. The U.S.
waste exchange industry lias developed more recently, and ity success rate is
only about 10 percent. A comprehensive review of foreign and U.S. background
and experience in waste exchange has recently been published.
Constraints on successful waste exchange include long transport distance
between the generation and reuse points, and cost of waste purification prior
to reuse. Factors which enhance waste exchange include the inherent value of
the material, high concentration and purity, quantity and reliability of
availability, and high offsetting costs for ultimate disposal.
Due to transportation cost factors, most waste exchanges operate on a
local, state or regional basis. Of the top ten states in terms of volumes of
hazardous wastes generated, four (Illinois, Indiana, Michigan and Ohio) are
located in the midwest, as are seve'n of the 28 known Waste Exchanges.
Waste exchanges may be operated by government bodies (e.g., Illinois,
New York), trade associations suchias State Chambers of Commerce, individual
industrial companies to handle their specific wastes, or as private, profit
oriented ventures. This latter approach appears most successful, due to both
i
confidentiality aspects and aggressive marketing techniques. Confidentiality
is often of industry concern, for two reasons;
1) to avoid alerting competitors to proprietary information which is
perceived to give the generator an economic edge, and
2) Industry may feel that despite good intentions, a regulatory body
may use "inside information" against the generator.
3.30
-------
Some waste exchanges ot'Cer the opportunity Tor the generator to approve a
proposed user in a viiste exchange activity.
The general categories of wastes which have been Kuccc-ssfully exchanged
to date in the U.S. include concentrated acids, alkalis, solvents, catalysts,
oils, other combustibles (for fuel value), and wastes with high concentration
of metals. Other, more specialized materials have also been successfully
exchanged. Examples include gypsurn wallboard (used as a soil conditioner),
scrap roofing shingles and trimmings, and calcium hypochlorite. However,
solvents and waste oils appear to be the most highly sought materials for
waste exchange. An example listing from a waste exchange bulletin is pre-
sented in Table 3.3. Such bulletins normally list both materials available
and materials sought. Although on an industry-wide basis it has been esti-
mated that with available technology only about 3 percent (6 million metric
tons/year) of the total U.S. hazardous wastes volume generated has potential
for waste exchange, the percentage in selected industrial categories is much
higher (Table 3.2). In general, waste exchanges take place from
larger companies using continuous manufacturing processes to smaller companies
using batch processes; from basic chemical manufacturers to fonnulator; and
from industries with high purity requirements (e.g. Pharmaceuticals) to those
with low purity requirements (e.g. paints).
Table 3.2 Categories of Industry Producing Hazardous Wastes With Significant
Potential for Waste Exchange and Reuse (USEPA, 1977)
Industry Category
Pharmaceuticals
Paints and Allied Products
Organic Chemicals
Petroleum Refining
Small Industrial Machinery
SIC Code
2831, 2833
285x
2865, 2869
2911
355x
Estimated Percent
With Reuse Potential
95
40
25
10
20
3.31
-------
'Tebia 3.3 PartUl Eiaopl« Listing tr5rail!,.vv.;.,|j
J^3W fftuso
C«SiUC2j B«« V Of
(itnta
Cas»;i»7 is go
LsesiKM «i=iffK>
COPS 8AM*
ilm l»l«J (did
evtftajw east
-------
3.7 CONCLUSIONS
The potential recovery strategies for the various classes of wastes are
summarized in Tables 3.4 and 3.5. The areas having the greatest potential
for recovery arc:
energy recovery from concentrated organic liquid wastes, e.g.,
incineration of waste organic liquids and oils
. recovery of materials from concentrated organic liquid wastes, e.g.,
distillation and recovery of waste solvents
recovery of metals from industrial sludges and metal plating wastes,
e.g., recovery of chromium, copper and nickel from spent plating
baths
It appears that the following techniques also have potential for development
and should be investigated further for possible application for material and
energy recovery:
:
-------
Detailed design and analysis of resource recovery facilities are directly
dependent on the specific nature, volume and composition of the waste to be
treated. Economic feasibility of resource recovery is highly sensitive to
such factors as value of recovered products, transportation and storage
costs. Transportation and storage at a recovery facility may involve special
risks not present at facilities primarily designed for disposal.
3.34
-------
Figure 3.1
Recover7 °* He Win froa Sludges
(Source: Shuscer Et al., 1979)
Metal
Sludges
Acid
Hatal
Hydroxides
-------
Figure 3.2
Recovery of HBteriel & Energy froa Haste Solvents
(Source: Shuster cs. oK, 1979)
Recovered
Solvents
Energy
Recovery
Scrubber
Solution
Impure
Solvents
Cleen
gas
Still
Bottoms
Ash 60
Secure Landfill
To Waste
Treatment
Plant
-------
Tabla J.4
Suiaa.iry of Resource & Energy Recovery Potential
for Hazardous Usstes (Inorganic) (Source: Shuuttr
et •!., 1979)
Typa of Wast®
101-Acid Soln. - no contaiain.
102-iic'icr"soln. - witii niecala
Heavy taatals (except Cr)
Ciuromiua
Noble raatsls
.^^^^^J" i c fc 1 a^J^icju o ?
TOJ-Acid soln. «• witts org.
Emulsified Qrg,
OtSCCXV€w potential
>r recovery 1
K
X
1
~Tr~
/.
x
X
csn
^3
X
K
3.37
-------
Table 3.5
Sucaaary of Resources 6 Ensrgy Recovery Potential
for Hazardous Wastes (Organic)
(Source: Shuater ec al., 1979)
Typa» of Waata
Concenc?ated Liqvuids
203.-clcan, halogcnated
202-clesn, non-balogenatad
203-clean, solvent mixtures
204-Dlsty, halogenated
20S"Dirty, non-ftsloganatetj
206-Dicty, sol\?erie taiseures
Dilute Aqueous Eolrtions
jrn-?.eadTTy~o5T5i zoci , ha log .
212-ReaAi.Vy osidt'EotS, non-halog.
213-oifficult to oxid.. halog.
2i<-Dlffic«lt to QKid., non-halo>3.
Ocgjsnic Solids
2"2i-salts and other solids
222-Tars artd cesldtaa
223-Sludgss
Organic Gases^^4®^8
231-coKTj«iaei5I©~"
Sgaelai tfastas 1
;JT!t-str6h'g oxidizing agents
312-Explosives 1
313-Diologicai wsstea
Direct recovery"]
or reuse |
X
X
X
X
X
K
X
X
«_
Raw material j
for secondary use]
X
X
X
K
X
X
X
Mrmni
"-• - — • ••" • •- ' 1
Energy recovery
K
K
X
K
K
K
~—
X
K
X
c
o
••*
A-l
3
-< -I
-1 O
O I'
£).*»
a o
•rf 0
9)
• W
3
.»»<
nix>w natsntiai j
for recovery |
X
X
K
sz
X
X
X
3 38
-------
REFERENCES
Battelle Memorial Institute, Program for tho Management of Hazardous Wastes,
Vol. I, EPA/530/SW-54c-l, PB 233 630 (1974).
Besselievre, E.B., "The Treatment of Industrial Wastes", McGraw-Hill Book
Company, New York (.1969).
Bocz Allen Research Inc., "A Study of Hazardous Waste Materials, Hazardous
Effects and Disposal Methods", Vol. II, EPA-670/2-73-15, PB 221 466
(1973).
Booz Allen Research Inc., "A Study of Hazardous Waste Materials, Hazardous
Effects and Disposal Methods", Vol. Ill, EPA 670/2-73-16, PB 221 467
(1973).
Boucher, F.B., ct^ a^l., "Pyrolysis of Industrial Wastes for Oil and Activated
Carbon Recovery", EPA 600/2-77-091 PB 270 961.
Cana, J.W., Proceedings of the 14th Industrial Waste Conference, Purdue
University, p. 26 (1959).
Federal Environmental Agency (West Berlin), "Disposal of Hazardous Wastes,
Manual on Hazardous Substnnces in Special Wastes", NATO CCMX Report //55,
PB 270 591 (1976).
Fisco, R.A., Proceedings of the 15th Industrial Waste Conference, Purdue
University, p. 15 (1960).
Folks, N.E.t et_ al., "Pyrolysis as Means of Sewage Sludge Disposal", J.
Env. Eng. Div., Aug. 1975, EE4 11518 607-621.
Genser, J.M. , et^ a_l. , "Alternatives for Hazardous Waste Management in the
Organic Chemical, Pesticides and Explosives Industries", EPA/530/SW-
145c2, PB 276 170, (1977).
Gurnham, C.F., "Principles of Industrial Wastes", John Wiley & Sons, Inc.,
New York (1955).
Gurnham, C.F., "Industrial Wastewater Control", Academic Press, New York
(1965).
Hall, E.P., _et aJL., "Recovery Techniques In Electroplating", Plating and
Surface Finishing, 65, 2, 49 (1978).
Hitchcock, D.A., "Solid Waste Disposal: Incineration," Chetn. Eiig., 185-194,
May 21 (1979).
Humenick, M.J. and Davis, B.J., "High Rate Filtration of Refinery Oily
Wastewater Emulsions", Jour. Witer Poll. Control Fed., 50, 1953 (1976).
3.39
-------
lannotti, J.E., e^t aj.. , "An Inventory of Industrial Hazardous Waste Genera-
tion in New York State", New York State Department of Environmental
Conservation Technical Report SW-P14 (1979).
Leonard, R.P., et al. , "Assessment of Industrial Hazardous Watite Practices
in the Metal Smelting and Refining Industry", Vol. 2, EPA/530/SW-i45c2,
PB 276 170, (1977).
Levin, J., et_ al_. , "Assessment of Industrial Hazardous Waste Practice -
Special Machinery Manufacturing Industries", EPA/530/SW-141C, PB 265
981.
Luthy, R.G., ejt_ aJL. , "Removal of Emulsified Oil with Organic Coagulants and
Dissolved Air Flotation," Jour, Water Poll. Control Fed., 50,331
(1978).
Nemerow, N.L., "Industrial Water Pollution - Origins, Characteristics and
Treatment", Addison-Wesley Publishing Company, Reading, Massachusetts
(1978).
Novak, R.G., "Eliminating of Disposing", Chemical Eng. 78, Oct. 5 (1970).
Ottinger, R.S., et_ aJL. , "Recommended Methods of Reduction, Neutralization,
Recovery of Disposal of Hazardous Wastes", Vol. V, National Disposal
Site Candidate Waste Stream Constituent Profile Reports—Pesticides and
Cyanide Compounds, EPA-670/2-73-053e, PB 224 583 (1973).
Ottinger, R.S., _et_ al..> "Recommended Methods of Reduction, Neutralization,
Recovery or Disposal of Hazardous Waste", Vol. VI, National Disposal
Site Waste Stream Constituent Profile Reports - Mercury, Arsenic,
Chromium and Cadmium Components, EPA 670/2-73-053f, PB 224 585 (1973).
Ottinger, R.S., _et al., "Recommended Methods of Reduction,, Neutralization,
Recovery or Disposal of Municipal Waste", Vol. XIII, Industrial and
Municipal Disposal Candidate Waste Stream Constituent Profile Reports—
Inorganic Compounds, EPA-670/2-73-053m PB 024 592 (1973).
Ottinger, R.S., _elt al.., "Recommended Methods of Reduction, Neutralisation
Recovery or Disposal of Hazardous Wastes", Vol. 12.
Patterson, J.W., and Haas, C.N., "Management of Hazardous Wastes: An Illinois
Perspective", Report to the Illinois Institute of Natural Resources
(1982).
Peters, G.O., et _al., "Assessment of Industrial Hazardous Waste Practices—
Electronic~Components Manufacturing Industry", US EPA SW-140c, NTIS PB
265 532 (1977).
Ross, R.D.j "Technology Options in Thermal Processing of Organic Hazardous
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3.40
-------
Santoleri, J.J., "Chlorinated Hydrocarbon Waste", Chem. Eng. P;og. Vol. 69,
No. 1, 68 (1973).
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of the Natl. Conf. on Complete Water Reuse, 2nd Waters Interface with
Energy, Air and Solids, AIChE, Chicago, 111. May (1975).
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Inorganic Chemicals Industry", EPA/530/SW-104c, PB 244 832 (1975).
Shustcr, W.W., jj_t a_l., "Technology For Managing Hazardous Wastes." New
York State Environmental Facilities Corp., Albany (1979).
Steele, W.R., "Application of Flue Gas to the Disposal of Caustic Textile
Wastes", Proceedings of 3rd Southern Municipal and Industrial Waste
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Steiner, J.L., £t al., "Pollution Control Practices: Air Floatation Treatment
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Tabakin, R.B., £t al., "Oil/Water Separation Technology: The Options Avail-
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Terry, R.C., jst aj^., "Waste Clearinghouses and Exchanges: New Ways for
Identifying and Transferring Reusable Industrial Process Wastes", Arthur
D. Little, Inc., US Environmental Protection Agency, PB 261 287 (1976).
"Report to Congress: Disposal of Hazardous Wastes", US EPA SW-115 (1974).
If
"Process Design Manual for Suspended Solids Removal" U.S. Environmental
Protection Agency - Technology Transfer. EPA 625/l-75-003a (1975).
Wadhawan, S.C., "Economics of Acid Regeneration - Present and Future", Iron
and Steel Eng., 55, 10 48 (1978).
i
i
Weber, W.J. Jr., "Physicochemical Processes for Water Quality Control",
Wiley-Interscience, New York (1972).
3.41
-------
CHAPTER 4
SECTION 1
DEVELOPING TECHNOLOGY FOR RECOVERY, REUSE, OR RECYCLE
Supercritical Fluid Extraction
Supercritical fluid extraction is a recently recognized separation
technique which has received much attention (Chem. Eng., 1979). Although
conditions vary for a given application, the supercritical fluid extraction
process has two fundamental operations. Tn the first step, the fluid, usually
at a pressure of 4,000-5,000 psi, and a density comparable to liquid hexane,
flows through the material to be treated in an extraction vessel. At this
elevated pressure its solvation power is greatly enhanced, and the fluid
becomes solute-laden. The fluid is then depressurized in a separation tank.
Because the solvation power of a supercritically compressed fluid varies with
respect to pressure, some of the extract will drop out of solution. Little
solvent residue is generally left behind in the extract.
According to the manufacturer, the process can extract materials such as
oils from natural products, organic pollutants from wasteivater, aromatic
isomers from mixtures, low-molecular weight materials from polymers, and
light components from coal (Chem. Eng. , 1982). It has also been applied to
the regeneration of wastewater adsorption beds (Eckert). Among the solvents
which can be used in the system are carbon dioxide, water, oxygen, ethlyene,
propane, and propylene (Chem. Eng., 1982).
Actual separation pressures, which can range from 500 to 3,000 psi,
depend on the economics of the application. Because a greater pressure
change requires more energy than a small one, a tradeoff exists between
the benefit of total solute recovery by.depressurization to ambient
4.1
-------
conditions and the cost of re-pressurizing the solvent for another pass through
the system (Chern. Eng., 1982).
Electrolytic Demulsificaticn
In the future, physical separation techniques will be required which
have capabilities surpassing those of conventional technology for separating
intimate liquid-liquid and liquid-gas mixtures (EPA, 1979). In several
large-scale industrial processes, the liquid-liquid mixtures occur in the
form of micro-emulsions of organic liquids in aqueous solutions. The treat-
ment of these emulsions by conventional means would require large batch
operations and generate voluminous quantities of sludge from which recovery
is uneconomical. There have recently been some promising developments in the
area of emulsion-breaking.
It has been shown that passing the micro-emulsion through a packed-bed
anode of iron (or low-carbon steel) chips in which ferrous ions are electro-
cheraically generated is an extremely effective destabilization technique.
The process requires simultaneous oxygenation by sparging or by electrolytic
evolution from a carbon anode (Weintraub and Gealer, 1977 and Weintraub,
Dzriechiuch, and Gealer, 1976). Such a process would have application in the
treatment of oily wastewater streams generated by the use of cutting oils in
industrial matching operations (Gealer, Golavou, and Weintraub). Other
possible applications include tertiary oil recovery, where alkali and sur-
factants are injected into wells and metal recovery from low-grade mineral
resources (Tavlarides, 1981), where solvent extraction is used as a concen-
tration device or as a pollution control step.
The mechanism by which the destabilization of micro-emulsions occu. •>
in the electrolyte process is only partially understood (Dzit.ciuch, Weintraub
4.2
-------
and Gealer, 1976), although the incentive for more research into the develop-
ment of a continuous process for the treatment of oil-in-water emulsions
exists. The process should have as. a primary requirement not only that it is
effective in destabilizing micro-emulsions but also that the sludge it gener-
ates should be as "dry" os possible to facilitate recovery of organics.
(IWERC Report, 1981).
Liquid Surfactant Membranes
Liquid membranes are formed when an emulsion of two immiscible phases is
dispersed in a third (continuous) phase. The encapsulated phase of the
emulsion is thus set apart from the continuous phase by the second phase of
the emulsion, which is immiscible with either the encapsulated or continuous
phases and constitutes, within this context, the liquid membrane. The stabi-
lity of the emulsion is maintained by the addition of surfactants and stabi-
lizing agents.
When developed for a given application, the three-phase system may be
1
used to facilitate separation of components in a mixture by selective diffu-
sion of the desired component from the contir. aous phase to the encapsulated
phase or vice versa. Following this transfer, the three phases can be
separated by first settling and separating the emulsion and the continuous
phase, and then breaking the emulsion (Wasan, 1982).
I
Liquid surfactant membranes have been shown to be of use in recovering
phenol, ammonia, organic acids, amines, and hydrogen sulfide from wastewater
(Cahn and Li, 1974; Cahn, Li, and Miday, 1978; and Li, Cahn, and Shrier,
1973). The separation of inorganic ions such as chromium and copper from
solution has also been studied (Hochhanser, 1975; Strzelbicki and Charewica;
and Senkan and Stauffer, 1981). Use of this technology is curbed by a lack
4.3
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of information pertaining to mechanisms which can be used to maximize flux
into and capacity within the receiving phase, and an understanding of the
relative impact of process variables on these mechanisms (Wasan, 1982).
Solidification/Encapsulation
The process of solidification and encapsulation involve the deactivation
and immobilization of a liquid or semi-solid (such as a sludge by converting
it to an inert mass suitable for landfill disposal (Senkan and Stauffer, 1981
and Patterson and Haas, 1982). For hazardous wastes which cannot be other-
wise detoxified or incinerated, these processes are the only environmentally
sound method of preparation for storage, and therefore promise to again rank
among the most important disposal techniques (Senkan and Stauffer, 1981).
Encapsulation is a process in which a liquid is encased and entrapped by an
impermeable coat, such as polyethylene or polybutadiene. In solidification,
a gelling agent such as cement or lime is added which chemically reacts with
the waste to form an impermeable mass. Several technologies exist for these
processes (Patterson and Haas, 1982).
The major wastes currently treated by solidification and encapsulation
processes are toxic and soluble inorganics and stack-gas-scrubber sludges
(Pojasek, 1979). While short-term leaching studies indicate that the mate-
rials produced by the processes may be stable, little information is avail-
able on their stability during the contact with leachate or water over long
periods of time (Patterson and Haas, 1982).
The solidification/encapsulation technologies currently in use are not
compatible with all wastes. Organics and strong oxidants are incompatible
with the majority of these technologies, although toxic anions and acidic
materials in a waste may also be cause for its incompatibility with a given
4.4
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process (Pojasek, 1979). In some cases, the mass which results following
treatment is flammable or may deteriorate upon contact with organic solvents
(Senkan and Stauffer, 1981). Due to the disadvantages associated with cur-
rently available technologies, the development of improved methods is deslrab
Dissolution
Dissolution may be defined as the complete or partial transfer of one
or more components from a solid phase into a liquid phase in contact with the
solid. The reaction involves some degree of chemical transformation (solva-
tion, ionization, oxidation) of the species being dissolved (Noyes Data
Corp., 1978). Although dissolution reactions are used in nearly all areas
of chemical processing, there has been recent interest in the in-situ disso-
lution of uranium (Tavlarides) from ore and of bitumen from tar sands
(Shahinpoor, 1982).
In the case of in-site leaching of uranium from underground deposits,
the subsurface deposit is flooded with leach solution and then pumped to the
surface ready for uranium recovery. Advantages of this method are a signi-
ficant reduction of processing costs and minimal disturbance to the surface
conditions, as well as production of a relatively small volume of waste
requiring disposal (Tavlarides, 1983).
The goal of in-situ bitumen recovery is to reduce the viscosity of the
bitumen while it is in place, by heating and/or diluting it, and to subse-
quently collect the liquefied product. Several solvents capable of reducing
oil viscosity are available, although they are generally more expensive than
the oil produced. Economic success therefore requires a high percentage of
solvent recovery, which is often difficult to achieve. In certain cases,
water may be a suitable solvent (Shahinpoor, 1982)
4.5
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The in-situ dissolution of uranium is feasible only where the ore body
is contained within a rock formation which is relatively impermeable.
Groundwater contamination may otherwise be a problem (Tavlarides). Potential
environmental impacts of producing oil from tar sands appear, on the basis of
methods tested to date, to be similar to those of conventional oil field
operations (Shahinpoor, 1982).
Particle Conditioning
In the presence of water, solids have an intrinsic electrical surface
charge. Almost all matter dispersed in spent process water such as oil
particles, salt, biocolloids, inorganic colloids, etc., has a negative charge
which is repelled by the negative electrical surface charge of granular
media. In order to maximize filtration efficiency, these coulombic repulsive
forces must be regulated through control of the physicochemical properties of
the dispersed solids. The colloids must be destabilised into agglomerates
tough enough to resist redispejrsive hydraulic forces in the filter.
Historically, granular media filtration has been viewed as a polishing
step following a clarifier. More recently, direct filtration of highly
contaminated has been investigated. Results indicate a large savings in
capital, chemical, and sludge treatment costs may be realized. Charge neu-
tralization or reversal by adsorption of a destabilizing chemical to the
i
colloid is a key mechanism fo£ optimization of direct filtration. When
molecules of the added chemical attach to two or more colloids, aggregation
and bridging occurs, and agglomerates are formed which resist redispersion.
The processes are demonstrated in the case of removal of coke fines from
hydraulic decoking water. Coke fines are originally stabilized by negative
zeta potential. This charge is easily reversed by the addition of cationic
4.6
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poly-electrolytes. The polyelectrolytes, which also have good bridging proper-
ties, cause most of the solids to be enmeshed in a polymer. Upon addition of
a small amount of weakly anionic polyclectrolyte, the positively charged
particles are "collected" into massive, easily separable aggregates. Once
the aggregates are formed, the forces which bind them are strong enough to
resist redispersion by the hydraulic forces of direct filtration (Grutsch and
Mallott, 1977).
4.7
-------
Bibliography
Chem. En a.. Mar. 12, 1979, pp. 43-43.
"System is Designed for Critical-Fluid Extractions," Chem. Eng.., January
25, 1982, pp. 53.
Progress Report on Research Planning Task Group Studies-Separation Technology.
C.A. Eckert to R.S. Engelbrocht.
"Environmental Considerations of Selected Energy-Conserving Manufacturing
Process Options" (20 Volumes), A.D. Little, Inc., EPA-60G17-76-034,
Dec. 1976 - Aug. 1979.
Weintraub, M.H., and Gealer, R.L. "Development of Electrolytic Treatment of
Oily Wastewater," A.I.C.h.E. 70th Annual Mtg. N.Y., Nov. 13-17, 1977.
Paper No. 151.
Weintraub, M.H., Dzrieciuch; M.A., and Gealer, R.L., Ext. Abstr. No. 261,
149th Ktg. Electrochemical Society, Washington, D.C., May 2-7, 1976.-
"Electrolytic Treatment of Oil Waste Water from Manufacturing and Machining
Plants," by R.L. Gealer, A. Golavou, and M. Ueintraufa (Ford Motor Co.)
Report on Grant No. S804174, IERL/EPA (Cincinnati, OH.)
Tavlarides, L.L., "Refining of Non-Ferrous Metals" and "Electroplating,"
BI-Monthly Report IWERC, Mar. 16, 1981.
Dziecluch, M.A., Weintraub, M.H., and Gealer, R.L., Ext. Abst. No. 260, 149th
Mtg. Electrochemical Society, Washington, B.C., May 2-7. 1976.
Identification of Research and Planning Needs for Industrial Waste Management.
IWERC Report, Mar. 16, 1981.
Wasan, D.T., "Separation of Metal Ions by Accelerated Transport Through
Liquid Surfactant Membranes." Preproposal submitted to IV/ERC. January
8, 1982.
Cahn, R.P. and Li, N.N., "Separation of Phenol From Waste Water by the
Liquid Membrane Technique," Separation Sci. 9(6), P. 508-518, 1974.
Cahn, R.P. and Li, N.N., "Separation of Phenol from Waste Water by the Liquid
Membrane Technique," Separation Sci. 9(6), p. 508-518, 1974.
Cahn, P.P., Li, N.N. and Miday, R.M., "Removal of Ammonium Sulfide from
Wasre Water by Liquid Membrane Process," Env. Sci. and Tech., Vol. 12,
p. 1051, 1978.
Li, N.N., Cahn, R.P. and Shrier, A.L., U.S. Patent 3,779,907, Dec. 18, 3973.
4.8
-------
Hochhanser, A.M. "Concentrating Chromium with Liquid Surfactant Membranes,"
AIChE Syinp. Ser., 71(152) p. 136-142, 1975.
Strzelbicki, J. and Charewica, W. "Separation of Copper by Liquid Surfactant
Membranes, J. Inorg. Nucl. Cheni. Vol. 40, p. 415-421.
Senkan, S.M. and Stauffer, N.W., "What to do with Hazardous Waste,"
Technology Review 84(2), pp. 34-47, 1981.
Patterson, J.W. and Haas, C.N., Management of Hazardous Wastes: An Illinois
Perspective (Draft)s report to the Illinois Institute of Natural
Resources, 1982.
Pojasek, R.B., "Solid-Waste Disposal: Solidification." Chem. Eng. August
13, 14 (1979).
Noyes Data Corp. Unit Operations for Treatment of Hazardous Industrial
Wastes. Park Ridge, N.J. 1978.
Tavlarides, L.L., "Process Modification Towards Minimization of Environmental
Pollutants in the Chemical Process Industry" Final report Submitted to
IWERC.
Shahinpoor, M. "Making Oil from Sand" Technology Review 85(2):48-54, 1982.
Grutsch, J.F. and Mallott, R.C., "Optimizing Granular Media Filtration"
CEP.. April 1977, pp. 57-66.
4.9
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CHAPTER 5
SECTION II
SORPTION
5.1 INTRODUCTION
According to Geankoplis (1978), there are presently many chemical
process materials and biological substances that occur as mixtures of
different components in the gas, liquid or solid phase. If it is desired to
remove one or more of these components from its original phase, another
phase must be contacted.
The term sorption includes both adsorption and absorption and refers to
a process in which a solute(s) (mixture component) moves from one phase and
is accumulated in another. Adsorption occurs when material is collected at
the interface between two phases. Adsorption can occur between a liquid-
liquid, gas-liquid or liquid-solid interface (Web^r, 1972). In absorption,
if
the two phases are brought into contact such that the mixture components can
diffuse from one phase to another, during the contact of the two phases, the
components of the original mixture redistribute themselves between the
i
i
phases. The following chapter is,divided into the following sections:
1. Absorption
2. Adsorption of Inorganic and Organics
3. Adsorption of Gases
5.2 ABSORPTION
The absorption of gases in liquids is one of the most frequently used
techniques for controlling the composition of industrial waste gases prior
to their discharge to the atmosphere. Waste gases are generally a mixture
of gaseous components, some of which are soluble in a selected liquid phase.
Direct contact of gas with liquid enables mass transfer to take place
5.1
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between the phases in directions governed basically by the concentration
gradients of the individual components.
The rates of mass transfer between the gas and adsorbent are determined
mainly by the amount of surface area available for absorption. Other
factors governing the rate of absorption, such as the solubility of the gas
in the absorbent and the degree of chemical reaction, are characteristic of
the constituents involved and independent of the equipment used. (U.S. EPA,
1978).
Mass transfer between two fluids is carried out by eddy diffusion in
the bulk of each phase and by molecular diffusion close to the interphase
boundary. It is assumed that complete equilibrium is established instantar
neously at the boundary, and that from this boundary, active spacies are
transported deeper into each phase by molecular diffusion followed at some
depth by mixing of isolated elements caused by eddy currents in the bulk
»
phase. Eddy diffusion is orders of magnitude faster than molecular diffusion.
The overall mass transfer rate is therefore controlled by mass fluxes
within the molecular diffusion layers.
Using several basic assumptions, two mathematical models hive been
developed. The simpler theory is based on the assumption that molecular
diffusion in both phases is predominantly in thin layers with laminar flow
conditions in which the concentration gradient is invariable with time.
Lewis and Whitman, adopting these steady state assumptions in both laminar
layers, developed a two film theory.
Since in many cases the concept of laminar steady flow cannot represent
the true nature of the process, the conditions of unsteady molecular diffusion
have been incorporated into more advanced models. It is assumed that an
5.2
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element of liquid stays in contact with the gas at an interphase boundary
for a limited time. After this, it is transported by eddy currents into the
bulk of the phase and replaced by another element initially with a uniform
concentration distribution. During the contact period, active species
diffuse into an element developing a concentration gradient which changes
both with time and position. (Bettelheim, et al. 1978).
In most cases, absorption of one component is simultaneously accompanied
by the desorption of another. Deliberate desorption can be achieved by a
change of physical conditions, stripping of the liquid with inert gas (or
steam), or by chemical decomposition of the sorbent. Absorption followed by
desorption constitutes a cyclic operation which allows reuse of the sorbent
and acts as a device for separation and concentration of the selected gas.
(Bettelheim, e£ .aJL. 1978).
Gas absorption equipment is designed to provide thorough contact
between the gas and liquid solvent to permit interphase diffusion of the
materials. Contact may be provided by various types of equipment, the most
common being plate and packed towers.
Plate towers employ stepwise contact. Several plates or trays are
arranged such that gas is dispersed through a layer of liquid on each
plate. The number of plates required is dictated by the difficulty of the
mass transfer operation and the desired degree of absorption.
Packed towers are filled with a packing material having a large surface
to volume ratio. The packing is wetted by the absorbent, providing a large
liquid film surface area for continuous contact with the gas.
The flow through plate and packed towers is usually countercurrent,
with the liquid being introduced at the top and the gas at the bottom. This
5.3
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arrangement results In Che highest possible transfer efficiency.
Spray towers and venturi scrubbers have more, limited application to gas
absorption. Spray towers dispense liquid absorbent in a spray through which
the gas is sent, while venturi scrubbers contact the gas and the absorbent
in the throat of a venturi nozzle. The gas-liquid mixture then enters an
entrainment separator in which centrifugal force separates the liquid droplets
from the gas.
Packed and spray towers introduce lower pressure losses than do plate
towers, and there is a high pressure drop associated with the operating
velocities of the venturi scrubber. Power requirements for venturi scrubber
operation are consequently large. Although spray towers have the advantage
of removing particular matter without plugging, they provide the least
effective mass transfer capability and their use is restricted to applications
requiring only limited removal of highly soluble gases. Venturi scrubbers,
If
also highly efficient for particulatp removal, are preferred for removal of
a highly soluble gas from a dirty gas stream.
Because spray towers and venturi scrubbers have limited application to
absorption, packed or plate towers are usually the equipment of choice. A
comparison of these two types of equipment is given in Table 5.1. (U.S.
EPA, 1978).
TABLE 5.1 COMPARISON OF PACKED ANDJ PLATE TOWERS (U.S. EPA, 1978)
1. Packed towers are less expensive than plate towers when materials of
construction must be corrosion resistant.
2. Packed towers have smaller pressure drops than plate towers designed
for the sane throughput.
3. Packed towers are preferred for foamy liquids.
4. Packed towers usually have a smaller liquid holdup than plate towers.
5.4
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5. Plate towers are preferred when the liquid contains suspended solids
since plate towers are more easily cleaned.
6. Plate towers are preferred for larger installations because they minimize
channeling and reduce tower height.
7. Plate towers are more suitable when the process involves appreciable
temperature variation, since expansions and contractions due to tempera-
ture changes may crush the tower packing.
8. Plate towers are preferred when heac must be removed, because cooling
coils are more easily installed.
9. Packed towers are preferred in sizes up to 2 feet in diameter if other
conditions are nearly equal.
5.2.1 Limiting Technology
In general, absorption is most efficient under the following conditions:
1. The vapors to be absorbed are quite soluble in the absorbent.
2. The absorbent is relatively nonvolatile.
3. The absorbent is noncorrosive.
4. The absorbent has low viscosity.
5. The solvent is nontoxic, nonflammable, chemically stable, and has
a low freezing point.
The rate of mass transfer between the absorbent and the gas is dependent
on the amount of surface area available for absorption. The solubility of
the gas in the absorbent and the degree of chemical reaction which takes
place are characteristics of the constituents involved. Gas absorption
equipment must be designed to provide adequate contact between the gas and
absorbent liquid to permit interphase diffusion of the organic vapors (U.S.
EPA, May 1978).
Selection of a suitable liquid solvent and the determination of the
limits of absorp-ion efficiency are based on solubility data. In most
cases, no formula is available for calculation of the solubility and only
tabulated or graphical data can be used.
5.5
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5.2.2 Recycle, Reuse, Recovery Applications: Organics
Many industrial processes which employ phenol 01- phenolic resins are
faced with the problem of toxicity and oaor problems arising from the evolu-
tion of phenol and phenol-derived volatile substances into the air. A method
developed for substantially reducing this atmospheric contain:),isLion consists
of absorbing the contaminants in an aqueous solution of a water soluble
phenol-formaldehyde resin and then condensing the mixture of absorbing resin
and absorbed contaminants to fosra an augmented resin by-product (Baker, 1975).
Gases contaminated with vapors from volatile organic liquids may be
recovered by contacting the vapor-containing gas with an absorbent sponge oil
in an absorbing tower. The sponge oil, rich in absorbed vapors, is conveyed
to a flash tank wherein the absorbed vapors are removed and recovered.
Following this process, the sponge oil can be successfully reused (Haines,
1975).
Kichols (1973) describes a low-temperature recirculating absorption
system capable of 90% hydrocarbon recovery and designed to recover vapors
present in saturated vapor air mixtures from the loading and storing installa-
tions of oil companies. The system consists of an absorber and components
which condition the vapors and liquid, improve absorption efficiency, reduce
thermal losses, and/or improve system safety. In the system, incoming vent
gases are saturated with fuel *nd the entrained liquid is allowed to settle
out before passing to an air compressor. The gases are brought to 45 psig
and approximately 300°F as they pass from saturator to compressor. They
then proceed to an aftercooler where temperature is reduced to an ambient
level. From the aftercooler, they pasn through a bubble bar and into an
absorber where they are absorbed by sprayed gasoline.
5.6
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5.2.3 Recycle, Reuse, Recovery Applications: Inorganics
When plastic wastes are burned in an incinerator, they tend to exhaust
a dark smoke resulting from incomplete combustion. In the case of polyvinyl
chloride (pvc) incineration, serious corrosion of equipment as well as air
pollution by hydrogen chloride gas will occur. Oda, e£ al. (1975) devided a
disposal system which results in recovery of hydrochloric acid from pvc
wastes. The process begins with carbonization of plastic wastes for about
40 minutes at 280°C to 300°C to reraove the chlorine from vinyl chloride.
Hydrochloric acid generated by the process is absorbed by water.
C0» and H-S may be removed using aqueous ammonia with production of
ammonium sulfate which may be recovered for sale as a fertilizer. Monoe-
thanolamine is used to remove C0_ from flue gas for its recovery or for the
purification of flue gas to nitrogen.
SO. can be removed by liquid absorption and purified for later collection,
compression, and resale. The Sulphidiise process uses a mixture of tylidine
and water and produces by-products of sodium sulfate and pure SO,,. In
another process designed to remove S0« from smelter gas, dimethylaniline is
i
the absorbent used to remove the gas from the stream, producing a by-product
of either dilute sulfuric acid or liquid S02 (Ross, 1972).
Within the past several years, a great deal of work has been done with
gas/solid absorption systems, particularly with regard to sulfur dioxide
(SO ) removal. These processes should not be considered for streams of low
flow, however, the catalytic oxidation process developed by Monsanto passes
flue gas, following particulate removal, through a vanadium pentoxlde
catalyst. This results in the production of a 77 percent sulfuric acid
solution.
5.7
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In the alkalized alumina process developed by the U.S. Bureau of Mines,
flue gas is passed through a fluid^.zed bed of alkalized alumina. The bed
reacts with the SO- in flue gas at temperatures of 300 to 350°C, resulting
in its conversion to sulfate. After treatment with a suitable reducing gas,
hydrogen sullied (H2S) gas is produced. The H?S is processed through a
Claus plant to bring about its conversion to elemental sulfur (Ross, 1972).
5.3 ADSORPTION
Adsorption on carbon has been known for a long time (Hasler, 1974),
however, its application in the field of municipal and industrial wastewater
treatment has become common only in recent years.
The term activated carbon applies to any amorphous form of carbon that
has been specially treated to give high adsorption capacities. Basically
tiiere are two forms of activated caibon: powdered and granular. The former
are particles that are less than U.S. Sieve Series No. 50, while the latter
are larger (U.S. EPA, 1971a). Typical raw materials, from which activated
carbon is made include coal, wood, coconut shells, pulp mill residues,
petroleum base residues, and char from sewage sludge pyrolysis. These
carbon materials are activated through a series of processes which include
(Cheremisinoff and Morressi), 1978:
1. Removal of ail water (dehydration);
2. Conversion of the organic matter to elemental carbon driving off
the non-carbon portion (carbonization; and
3. Burning off tars, methanol, and other by-products at high tempera-
tures (750-950°C) (activation).
Adsorption involves the interphase accumulation or concentration of
substances at a surface or interface (Weber, 1972). The process can occur
5.8
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as an interface between any two phases, such as, liquid-liquid, gas-liquid,
gas-solid, or liquid-solid interfaces. The material being adsorbed is
called the adsorbate while the adsorbing phase is termed the adsorbent.
There are two types of adsorption: physisorption and chemisorption.
The former occurs because of weak Van der Wall's forces while chemisorptiqn
is a result of a chemical interaction between the adsorbent and the adsorbate.
Physisorption is characterized by a relatively low energy of adsorption and
may be multilayered. Chemisorption processes, however, exhibit high energies
of adsorption.
The adsorption process can be affected by many factors, some of these
include (Cherenisinoff and Morressi, 1978):
1. The physical and chemical characteristics of the adsorbent, i.e.,
surface area, por> size, chemical composition, etc.
2. The physical and chemical characteristics of the adsorbate, i.e.,
molecular size, molecular polarity, chemical composition, etc.
3. The concentration of the adsorbate in the liquid phase.
A. The characteristics of the liquid phase, i.e., pH, temperature,
etc; and
5. Residence time of the system
5.3.1 Factors Affecting Adsorption: Inorganics
The surface area of the activated carbon plays a critical role in the
removal of inorganics by adsorption. It may typically range from 500 to
1400 B /g with some carbons having surface areas up to 3,500 m /g. Another
important parameter affecting the adsorption process is the chemical nature
of the surface of carbon. This chemical nature varies with the carbon type
and can Influence attractive forces between molecules. For the most part.
5.9
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activated carbon surfaces arc nonpolar making the adsorption of inorganics
difficult (Chercinisinoff and Morressi, 1978).
5.3.2 Regeneration Operation: Inorganics
Wastewater treatment with activated carbon involves two major separate
process operations, namely, contacting and regeneration. During the first
operation, the water is contacted with the carbon. Impurities are removed
from the water by adsorption to carbon. After a given period of time, the
adsorptive capacity of the carbon is exhausted. Then the carbon is taken
out of service and regenerated, usually, by combustion. During this pro-
cess, the impurities are adsorbed for potential recovery.
On some systems an additional process operation namely, backwashing may
be necessary. It is required in cases where suspended solids are trapped in
carbon beds causing severe head losses. Backwashings are more frequent for
downflou contactors, which may be designed xor suspended solids removal
also.
Regeneration of spent carbon is practiced in cases where a large quantity
of carbon is used. Thermal reactivation is the most common method used for
i
regeneration of carbon. Other methods include alkaline regeneration for
acid adsorbatcs, acid rogneration for basic adsorbates, stream regeneration
and solvent regeneration.
5.3.3 Recycle, Recovery and Reuse Applications: Inorganics
Activated carbon is used in water treatment to remove organics that
cause odors, tastes and other detrimental effects. It is used in municipal
and industrial wastewater treatment for removal of dissolved and/or hazardous
organics. In addition, activated carbon is used as a recycling media for the
recovery of valuable substances from certain industrial effluents.
5.10
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The major applications of activated carbon in wastewatsr treatment
ir.^iude:
1. Silver and Gold Processing Plants (Cheremluinoff and Morrissi,
1978).
2. Inorganic Chemical Industry (Suisi, et_ _al_. ^.970; Taushkano, et al.
1974).
3. Electroplating Industry (U.S. EPA, 1971b; Smithson, 1971).
4. Refineries (Loop, 1575)
5. Various Industries With Metal-laden Effluents (LinsCedt, et al.
1971; Cherewisinoff and Hablb, 1972; Netzer, £t al_. 19/4).
Various inorganic substances from the above-listed industries are
removed from the effluents and possibly recovered through the use of activated
carbon treatment. The degree of adsorption of these inorganics on carbon and
the final recovery may vary from species to species. The major group of
inorganics which are recovered through activated carbon treatment are taetals.
By product recovery is advantageous for valuable substances and also in cases
where regeneration of carbon results in low recovered adsorptive capacity of
carbon.
5.3.4 Factor Affecting Adsorption: Organics
The adsorption capacity for organic solutes is thought to be a function of:
1. Adsorbate properties such as functionality, branching or geometry,
polarity, hydrophilicity, dipole moment, molecular weight and size, and
aqueous solubility.
2. Solution conditions, including pH, temperature, pressure, adsorbate
concentration, ionic strength, and the presence of background and
competitive solutes.
5.11
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3. The nature of the adsorbent, such as surface area, pore size and distri-
bution, surface distribution, and surface characteristics (Miller, 1980a)
5.3.5 Adsorbents-Activated Carbon and Resins: Organics
Activated carbon is a term used to describe materials prepared from raw
materials such as wood, lignite, coal, bone petroleum residues, and nut shells
which exhibit a high degree of porosity and extremely large internal surface
area. Activated carbon has found a wide commercial application as an adsor-
bent due to its ease of production, reasonable cost, and regeneration capabi-
lity.
Little quantitative information is known about the surface characteris-
tics of carbon ar.d its influence on organic adsorption selectivity. These
characteristics are important to adsorption of specific solutes. Two types
of surface interactions are thought to predominate. The first is that of
van der Waal force interactions, hycirophobic in nature, and occurring on a
majority of the surface. The second type occurs at the more reactive edges,
and may be characterized by positive physical and perhaps chemical interac-
i
tions due to hydrogen bonding and electrostatic forces. This second type of
interaction occurs at a small fraction of the total surface area. Specific
adsorptions will result from the presence of oxides, hydroxyls, and other
groups on the surface. Activated qarbons produced by different processes
probably differ in their adsorptivity as a result of their different energy
potential and the extent of their heterogeneous sites (Miller, 1980a).
Snoeyink, £t al. (1979) found that the nature of sorption sites can
vary significantly between different carbons, even though they have similar
total surface areas. Their results indicate that phenol sorbs more
5.12
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extensively on a coal-based carbon than on a coconut-shell carbon at low con-
centrations. Recommendations were made for study in the areas of the sorptive
behavior and characteristics of activated carbon, the types of functional
groups on the surface, and possible alteration of the surface to produce a
more efficient adsorber for a given purpose.
El-Dib, £t al. (19V9) states that little is known about the adsorption
characteristics of soluble aromatic hydrocarbons on granular carbon and its
efficiency in the removal of such orgar.ics. In a study of benzene, toluene,
o-xylene and ethylbenzene, they found that these compounds were adsorbed in
accordance with the Freundlich model, and that the parameters K and 1/n
reflect the effects of chemical structure, solubility, and competitive inter-
actions on the adsorption process. In the case of a mixed-solute solution,
they found that uptake of each compound was considerably reduced, although
the order of adsorption was the same.
The use of polymeric adsorbent resins should be considered in cases
where the economics of solvent or chemical regeneration of the adsorbent is
favorable. Polymeric adsorbent resins are similar in size, shape, and appear-
ance to conventional ion exchange resins, but differ in the respect that
they contain no ionically functional sites. There are two basic families of
adsorbent polymers available: one is based on crosslinked polymethacrylate
structure, while the other is based on a crosslinked polystyrene structure
(Fox, 1979). Although capital costs of synthetic adsorbent systems and those
of activated carbon are comparable, operating costs indicate that polymeric
adsorbent methods are more economical than carbon systems when the level of
dissolved organics is high (Stevins and Kerner, 1975). An attractive feature
of synthetic resins is that they can, at least theoretically, be designed and
5.13
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manufactured for i specific adsorption application (Ki.n, ejt^ al. 1976).
It has been demonstrated that Amberlite XAD polymeric adsorbents can
remove substantial quanuities of phenolic compounds from aqueous solutions
with the added benefit of being easily regenerable with nonaq-jeous solvents
or caustic solution. This permits the recovery of a useable form of phenolic
material in many cases. Crook, et_ al. (1975) studied the results of flow
rate, concentration, temperature, and pH on phenol removal. They found that
at 6700 ppm influent phenol concentration, the capacity of Amberlite XAD-4
polymeric sorbent for phenol is (to 1 ppm leakage) 87 g/1, while at 3000 ppm
influent concentration the capacity decreases to 72 g/1. Cumulative phenol
leakage was found to be slightly higher at 5°C than at 25°C. Although flow
rates were varied from rates of 2 to 4 bed volumes per hour, the resultant
phenol leakage was 0.1 ppm or less up to the break point. pH values of 3 and
6.45 were used to determine the effect of pH on phenol removal. Results
indicated that slightly better performance may be obtained in the lower pH
range- In another experiment Crook, £t al. (1975) tested the effect of bed
depth on removal of p-nitrophenol and found that a 15 inch bed depth column
of XAD-7 resin does not afford substantial improvement over a 9 inch bed
depth in either leakage or capacity at the flow rate of effluent studied.
Removal of Eisphenol A was also studied using both the XAD-4 and XAD-7 resins.
These resins differ in polarity. It was found that the XAD-4 resins success-
fully treated 33.5 bed volumes while the XAD-7 treated 16 volumes. These
experiments were mentioned to illustrate the many variables which may or may
not effect removal of an organic compound from an aqueous solution.
The use of carbon adsorption, and more recently, polymeric resin adsorp-
tion for removal of organic contaminants from wastewater has proven to be
5.14
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effective. However, DiCiano (1980) states, with reference to carbon adsorp-
tion, that there are many unanswered questions regarding control of process
performance and that part of the problem originates from the variability in
composition and concentration of contaminants in waste streams. Regarding
polymeric resins, complex reactions involved in the adsorption process can
only be partially predicted. Laboratory feasibility studies, and in some
cases pilot studies under actual use conditions, are generally needed before
the appropriate resin and operating conditions for a specific application are
defined (Fox, 1978).
5.3.6 Regeneration and By-Product Recovery: Organics
Hiramelstein, et al. (1973) reviewed the various methods of in-place
regeneration of activated carbon. Reactive regeneration, by which phenol is
desorbed from the column by reaction with caustic soda, has been practiced.
In the plant where this took place, the regenerant solution was suitable for
recycle without farther treatment and an excellent example of an opportunity
for recovery, Phenol is recovered in the product stream, and the residual
caustic is used as a component in phenol production.
Solvent regeneration Involves ithe use of a solvent phase to desorb the
organics from the carbon, and is removed as in conventional recovery systems
by steam. The solvent may be recovered for reuse in subsequent regeneration
^
while the desorbed materials may be reintroduced into the process or refined
for reuse or sale. In some cases, the regenerated steam nay be recycled
without further processing. Unlike reactive regeneration, solvent regenera-
tion is feasible in cases where direct recycle of a regenerant stream is not
feasible. Separation of the solvent and recovered material may be accom-
plished by distillation, extraction, decantation, or precipitation. Recovery
5.15
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by steam treatment has been demonstrated by laboratory studies to be feasible
for waste streams such as those containinj; aci-tic acid, nrowatic acids,
chlorinated aroma tics, phenols, alcohols and esters.
Due to the high binding energies of carbon, thermal reactivation of
activated carbons is often the only successful moans of regenerating the
carbon. Thermal regeneration also leads to destruction of the adsorbed
species, making their recovery impossible. Baker, e£ aj_. (1973), however,
describes the use of carbon adsorption of sulfite effluent prior to oxidation,
followed by chemical regeneration of cresylics and return a valuable product
to the process in a full-scale plant situation.
Jensen (1980) describes a semi-continuous activated carbon system for
removal of dissolved acrylic monomers from wastewater. By using such a unit,
acrylic tnonoaers can be recovered at some value, and the wastewater is up-
graded for reuse. Three carbons were compared for suitability for removal of
COD loading in these wastewaters.
Phenolic compounds are bound to adsorption polymers by van der Waal's
forces. Parmele has shown this by measuring the enthalpy of binding mono and
dichlorophenols to Amberlite XAD-4 at -4 to -6 kcal/mole. This is within
the range for physical forces holding the phenolic to the adsorbent. -Small
energy inputs are required for desorption, the phenols can be easily recovered
by regenerating the resin. This is the key to the value of resins for waste
material recovery. Fox and Himmelstein (1974) discuss several applications
of polymer adsorption and regeneration for the recovery and recycle of phenol,
para-nitrophenol and phenoxy acid pesticide.
Stevens and Kerner (1975) state that the binding energies of synthetic
resins are lower than those of activated carbon for the same organic molecules.
-------
This would make recovery of organics from rasins more attractive than from
carbon, due to smaller energy inputs needed for dcsorption. Fox (1979) lists
organic solvents including acetone, methanol, isoproj/anol, end inorganic
solvent systems such as steam, aqueous caustic solutions, and aqueous acid.s
for resin regeneration.
Chlorinated pesticides such as endrin, DDT, 4-D, 2, toxaphene, and
polychlorinated biphenyls can be efficiently removed by adsorption onto an
adsorbent resin with polystyrene structure. One plant which manufactures 2,
4-D, and related herbicides practices recovery of phenoxy herbidicides and
their intermediates for recycle to the process. Regeneration is performed
with saturated steam. The resin Is regenerated with methanol, and the herbi-
cide and its intermediate is recovered by distillation.
Aqueous effluents from vinyl chloride and other chlorinated hydrocarbon
manufacturing plants contain up to 1% of a mixture of ethylene dichloride,
chloroform, and/or carbon tetrachloride. After steam regeneration of the
resin, the collected condensed organic phase can be either reused in the
plant or incinerated. Effluent streams from the production of benzene,
toluene, and xylene are usually contaminated by these organics. Recovery of
these compounds is carried out in a process scheme similar to that for
chlorinated hydrocarbons. From these examples, it is evident that polymeric
adsorbents may be used by industry for removal and recovery of chlorinated
pesticides, phenols, aliphatic chlorinated hydrocarbons, benzene, toluene,
and xylene (Fox, 1979).
5.3.7 Predicting Adsorption: Organics
Several approaches have recently been developed to relate characteristics
of molecular structure or a chemical property such as solubility to adsorption
5.17
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potential for activated carbon. Mar.es and Ho for applied tlio I'olanyi adsorp-
tion potential theory, originally developed to describe gas-solid adsorption.
Follow up studies have shown this technique to bo successful for describing
single, bi- and tri-solute tqiilibria, but testing is still limited. 'Problems
vith the application of the theory include the fact that the solubilities of
many organic compounds of interest are not readily available, while other
compounds are relatively soluble, requiring that a more complicated model be
used (DiGiano, 1980).
Although few multicomponent studies have been done, equilibrium models
have been developed. These include the Langmuir Competitive Model, which
maintains that adsorption sites are available to all adsorbates; the Langmuir
Semi-Competitive Model, which states that some sites are availabl" to all
absorbates while others are just available to most adsorbable material; and
the Ideal Solution Theory, which is developed from thermodynamic considera-
tion.
Each model was tested on its own bisolute systems, and little has been
done to compare the models on additonal systems. In a column study, all
three were unsuccessful in predicting relative loadings.
A predictive technique developed by Keinath, et al. to predict individual
component behavior was based on the assumption that increasing Langmuir b
constants are related to stronger adsorption. Tests were limited, and more
work Is necessary. This method could possibly predict the preferentially
adsorbed compound.
It may be possible to simplify the description of competitive systems
by grouping adsorbable components into a few broad classes according to their
equilibrium adsorption behavior. A single, synthesized equilibrium isotherm
5.IS
-------
for each class would be used in simulation of competitive adsorption. For
this to occur, a oethod must be found to account, for competitive behavior
which does not conform to that cxpc-cted babed upon slr.^lu component Isotherm.
Crittendcn end Weber found this to occur in a phenol-dodecylbenzenesulfonatc
(DBS). Phenol was absorbed to a far greater extent in a sinp.le solute system,
but competition favored adsorption of DBS (Arbuckle and Romagncli 1980).
Arbucklc and Romagnoli (19SO) used isotherm constants and chemical
solubilities to predict the preferentially adsorbed compound in 22 bisclute
activated carbon systems. Solubility predicted the preferred compound for 20
systems, while the Freundlich K constant was correct for all systems. The
amount of nonpreferred material displaced was in correlation with the absoluta
difference in K; the greater the difference, the more material displaced.
This information is useful in predicting whether or not a chemical will be
concentrated in a column's effluent and to minimize carbon consumption by
knowing the order the compounds leave'the column (important when removal of
a specific component is desired). They recommend -Mditional studies to (1)
determine effects of different relative solute concentrations, (2) evaluate a
wider variety of chemicals, and (3) evaluate multi-solute systems.
Because many of the equilibrium theories and theories for predicting
competitive adsorption currently in use are based on gas and vapor phase
adsorption, they have one major limitation: the presence of solvent during
solute adsorption is ignored. Belfort and Altshuler have adapted the solvo-
phobic theory, a general therrcodynamic treatment for describing the effect of
various solvents on reaction.rate constants and equilibria, to adsorption
(Miller, 1980b).
By using the same type of adsorbent and identical solution conditions,
5.19
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different workers have attempted correlation of single-solute adi»or{>t ivc
capacity with molecular weight, solubility, functionality, and position of
substitution. Although several general trend.-; are indicated, no one pararaelc-r
has etr.erged in predicting the dominant effect of adsorption. It is probably
not reasonable to expect a one-dimensional approach to provide a consistent
predictive correlation (Miller, 1980b).
Given single-solute or multisolute adsorption equilibrium, a reasonably
good description of mulcicomponent behavior may be obtained. There is a need
for an equilibrium adsorption theory which can predict, without experimental
observations, the preferential adsorption of organic compounds onto activated
carbon from dilute aqueous solutions (Miller, 1980a)c
5.3.8 Recycle, Recovery, and Reuse Applications
Compounds Recovered:
Polysterene Adsorbent Resins Toluene
Polychlorinated Biphenyls Xylene
Ethylene Bichloride Ethylbenzene
Chloroform Acrylic Monomers
Carbon Tetrachloride Phenol
Benzene, Toluene, Xylene Acetic Acid
Phenols Aromatic Acids
Para-Nitrophenol Chlo'rinated Aromatics
Phenoxy Acide Pesticides Alcohols
Chlorinated Pesticides Esters
Aliphatic Chlorinated Hydrocarbons Cresylics
Activated Carbon Hydrocarbons
Benzene Tar Acids
Tar Bases
Industries in which Recovery by Adsorption has been applied:
Pesticide Manufacturing
Organic Chemical Manufacturing
5.20
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1'et rociiernical Industry
faint Ir.d-.istry
Coke Plant
5.4 ADSORPTION: CASKS
The potential areas for future research in the adsorption of gasec arc:
1. AJsurbetit Properties
2. Regeneration Methods
3. Modeling Theory
A brief description of these areas follov,-s:
1. Adsorbents
In the recovery of organic gaseous air pollutant;,, activated carbon has been
by far the most effective adsorbent used. However, the adsorptive capacity
of any adsorbent is limited by:
- the surface area available for adsorption
pore size and distribution
temperature and pressure of. operating conditiu. -i
concentrations of influent brganics
desired recovery level (collection efficiency)
Exploration of the effect of different catalysts on the adsorbing surface
could result in a more effective and easy way to desorb (these catalysts
should inhibit stronger affinity onto the adsorbing surface for material to
be recovered).
Impregnation of adsorbents has proven successful in some cases and could
be further studied.
2. Regeneration Operation
In the regeneration process, modification of the systems and operating
procedures used in solvent recovery have already resulted in an improved
collection. However, this recovery is rarely optimized under given operation
5.21
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cond i t ions.
Vacuum s;tripping (Kenson, 1979) with steam has been recently been iliovn
to be a successful method of recover Jn^ hydrocarbons. However, sor.e problems
arose due to corrosion effect of the adsorber vessel, e.£., ?;any of the
materials recovered hydrolyzo slight Iv to generate i!tl when exposed to chlori-
nated solvent. A better understanding not only of physical properties but
also of chemical properties of both adsorbent and adsorbate is necessary.
The improved design of existing systems and their regeneration control
(this control should be based on regeneration capacity rather than tirae
cycle) would certainly give a better regeneration rate. It can also result
in corrosion reduction (Tarmole, «it_ _a_l. 1979).
An investigation of the regenerating media will shed more light on the
right choice of the regenerating agent.
Methods of predicting binding energy of solvent molecules to the adsor-
bing surface (the problem arises here when dealing with competing molecules
from a mixture of solvents) (U.S. EPA, April 1978) are needed.
3. Theory and Modeling
Theoretically, optimum adsorption is accomplished under the following
conditions:
low base-line concentration of effluents
containment of breakthrough emissions
efficient recovery of desorbed organics
containment of organics exhausted during
cooling and drying cycle
Since adsorption capacity is affected both by the properties of the adsorbent
and those of the adsorbate, and the conditions under which they are contacted,
5.22
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a better understanding of the properties of both adsorbent and adsorbate
would be beneficial.
A better method for predicting the preferential adsorption of competing
molecules (in a solvent mixture) and how they could be dcsorbed uorv effective-
ly is needed.
5.4.1 Adsorbents and Their Properties
Kach adsorbent has a preferential adsorption for adsorbates based on its
adsorptive Capacity and affinity for different materials (adsorbates). It is
this characteristic (selectivity) that is important for each adsorbent.
Selectivity and capacity can change the suitability of an adsorbent for
air pollution control usage, limiting some for special conditions, while
allowing broader application of others.
Chemical composition, ratio of surface area to volume, pore size and
distribution and granule (particle) size are the most important characteristics
of an adsorbent. The adsorption capacity is a function of these characteris-
tics, and is better defined with adsorption isotherms and/or adsorptive
capacity data at different operating conditions.
Depending on their chemical constitution and pore size distribution,
adsorbents can be classified into the fo-;r categories which are discussed
below.
1. Chemically Reactive Adsorbents
These adsorbents can also be impregnated with chemically reactive com-
pounds. The adsorption operation by these adsorbents is highly selective
and tends to be irreversible. It is an exothermic reaction which stops
when all active sites on the surface have reacted. The surface is then
covered with a unimolecular layer of vapor.
5.23
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Example: Soda lime (with or without activated carbon) is used in the
cheinitiorption of ethanoic .'icid, aci-tonitrilo, ac rylonitrile,
alkyl chloride, and vinyl propyl desulfide.
2. Polar Adsorbents
The adsorption process is caused by Van der Waal's forces on a chemically
non-reactive surface, having polar properties. These adsorbents are
less selective and the process is reversible. The heat released is
about 10 kcal/g. mole.
The adsorbing surface is saturated by several molecule layers. At fixed
vapor pressure, the adsorption decreases with increasing temperature.
Examples: Silica gel and activated alumina both have strong selectivity
for polar compound (H_0, olefins) and are generally used in
separation and purification processes.
The dielectric constant and the dipole moment of molecules characterize
their adsorption affinity. Affinity! decreases with decreasing dielectric
constant and decreasing dipole moment. However, it also decreases with
increasing Van der Waal's force.
i
The application of these adsorbents is mainly limited to the drying of
gases due to their strong affinity for water. Desorption generally
occurs with regenerative water steain followed by drying of adsorbent at
higher temperature.
3. Non Polar Adsorbents
The most important adsorbing non polar solid is carbon, which is effec-
tive in attracting non polar molecules such as hydrocarbons. Activated
carbon is used to remove hydrocarbons, odors and similar trace contami-
nates from gas streams. Activated carbon must be specially treated
5. 24
-------
before use, because adsorption of water vapor is very ser. Ativ* to the
presence ot polar impurities. Activated carbon usually ccr.talns S.O ,
A12, Fe00 , NaOH, KOH and adsorbed oxygen.
4. Molecular Sieves
Molecular sieves arc available as having polar and non polar properties.
They are effective in adsorbing low molecular weight or unsaturated
hydrocarbons from dry air at low concentrations. Adsorption of low
molecular weight saturated hydrocarbons (methane, ethane) by activated
carbon is more effective than by molecular sieves, but toe pooi in any
case for effective pollution control.
5.4.2 Regeneration Operation: Oases
The adsorbent bed must be regenerated for reuse after breakthrough has
be^n reached. The recove^ • of organic compounds generally occurs by stripping
(Kensen, 1979) them into easily condensable streams of gas. The conventional
methods of regeneration involve heated air, heated inert gas or heated stean:,
depending both on the adsorbent and the adsorbate properties. In the case of
use of noncondensable gas as a regenerative agentp the desorbea material can
be disposed of in several ways (U.S. EPA, April 1973). When using steam as a
regenerating agent many pollutants cannot be economically recovered due to
their high steam to solvent ratios. Adsorption/steam regeneration with
solvent recovery has been conventionally used in concentration above 500 pptn.
Using distillation on partially or totally soluble compounds is costly, and
moreover disposal of this polluted steam condensate can constitute another
form of environmental pollution if disposed of into sewers.
Some commercially available systems use hot nitrogen or scree other mel-
gases to desorb the organics from the carbon. Vaporized organics condense to
5.25
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a liquid, and are reused in the process or as a supplemental fuel. The inert
gas is then vented or reheated and recirculated to the adsorber.
Regeneration can also be accomplished by vacuum stripping (Kenson, 1979).
In a vacuum system, pressure is reduced to a point below the original partial
pressure of adsorbed material. Regeneration takes place rapidly at extremely
high concentrations. This method is used when there is hydrolysis of the
organics or formation of azeotrope with water, if the organics do not respond
sufficiently to low pressure steam regeneration, or if they have concentration
above combustion range. Inert gas regeneration is also used under the above
conditions. A cooling and drying period is necessary before the bed can be
reused for recovery.
Recent efforts of process engineers and equipment designers have been
mainly oriented toward improving the economics of solvent recovery operations.
So far the principal areas of interest have been (U.S. EPA, April 1973):
- Decrease in energy or fuel requirement for regeneration
Reduction of pressure drop during adsorption phase
Increase of adsorptive capacity by utilizing residual capacity of
adsorption zone
- Improved methods for ecovery of desorbed solvents,
5.4.3 The Adsorption Cycle: Gases
The adsorption cycle is a function of the adsorbent life, the bed length,
and the mass transfer zone. Vapor-phase activated carbon adsorption has
gained favor as a method of recovering valuable solvents from industrial
emission sources. The adsorption is usually a batch operation with multiple
beds. Upflow design is generally avoided because carbon particles can become
entrained in the exhaust at higher superficial velocities. The gas stream is
5.26
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pretreated to remove solids (dust, lint), liquids (droplets or aerosols), or
vapor (high inlet concentration or high boiling components) since these can
hamper performance. Pre'creatment with condensers Is generally advantageous
in reducing inlet concentrations. The following objectives are required for
high removal efficiency (Parmele, et al. 1979),
- Low base-line effluent concentrations (usually less than 10 ppm) .
Containment of breakthrough emissions. This is done by avoiding
premature breakthrough or by sending material emitted during break-
through to another vessel hooked up in series.
Efficient recovery of desorbed organics. This is usually achieved
by condensing the vapors and recycling the noncondensables from the
condenser back to the inlet of the online adsorber.
Containment of organics exhausted during the cooling and drying
cycle. This cycle prepares the carbon bed for renewed service.
5.4.A Adsorption Theory and Modeling: Gases
The adsorption operation is a method of controlling gaseous impurities
from industrial gas streams. The gas molecule is retained on a solid surface
by physical or chemical forces. These two types of adsorption are described
as follows:
Physical Adsorption
Physical adsorption occurs when gas molecules attract and hold each
other forming a multilayer of gas molecules (not more than a few
molecules thick) on the solid surface area. This is caused by Van
der Waal's forces at the gas-solid interface. The process is
exothermic (10 kcal/g-mole) in which the free energy of the gas
decreases.
5.27
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Chemical Adsurut ion—Chemisorptipn
Tills is also an exothermic process (10 kcal/g-mole) in which gas
molecules are held to the adsorbing surface by chemical bonding
(sharing of electrons). Cheraisorption results in only one layer of
molecules on the adsorbing area available.
The adsorption phenomenon occurs in two stages. First, there is rapid
and 100% removal efficiency, then breakthrough happens when this removal
efficiency falls below 100%. At this point outlet concentration is equal to
the inlet concentration.
A single vapor consists basically of a solvent and air. However, when
water vapor is present in the vapor, the mixture becomes ternary. At high
concentrations of water vapor in the mixture, interference occurs among the
solvent molecules and the water molecules adsorbing to the activated sites.
This same phenomenon occurs, although in a different way, in a mixture of two
or more solvents.
The presence or absence of water may be the deciding factor in choosing
the adsorbents. For example, when water vapcr IF. present in a gas stream,
adsorption of organic vapors cannot be effectively achieved with polar adsor-
bents (U.S. EPA, April 1973). The effect of the competition of solvents on
adsorption efficiency are not well understood.
In order to arrive at an optimum interaction between adsorption and
regeneration, it is necessary to understand the factors that affect the
performance of the adsorbent (activated carbon) during these two operations.
So far there is no method that satisfactorily predicts the performance of
adsorption systems from theory, although several have been proposed.
5.28
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It has been found that the average residence time of a molecule on the
surface increases with decreasing temperature and/or decreasing partial
pressure of the vapor.
Freundlich described the adsorption phenomenon in its early stage by tlu
following equation (U.S. EPA, April 1973):
V <= k P1/n (5.1)
where: k and n are Freundlich constants
This equation applies also to cheraisorption. This is common when an impreg-
nated carbon is used. The most common theory that is valid In describing
adsorption in the smallest pores is Polyanyi's potential (Parrcele, 1979)
theory which holds that for a fixed amount of adsorbed materialj the free
energy of adsorption, AF, is a constant and is a function of the relative
vapor pressure (P/P ) .
(5.2)
where: T = absolute temperature
Po = vapor pressure
P = partial pressure
R - ideal gas law constant
This relationship makes the use of isotherms possible in predicting
relative vapor pressures of a material in equilibrium with carbon at a
variety of temperatures.
5.4.5 Application rA Adsorption Operation in Industries: Gases
Adsorption is a particularly recoiamer.ded and useful technique when:
1. The solvent (containment) has recovery value.
2. The solvent is in extremely low concentrations.
3. The solvent gas may be noncombustible or nonflammable (below
25% of its lower explosive limit)
5.29
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Some of the applications of adsorption are used in:
surface coating (fabric or filter)
film casting
metal degreasing
dry cleaning
printing
rendering
food processing
chemical processing
- paint spray booth
bake ovens
Some of the principal adsorbents used are:
- activated carbon: hydrocarbons, odors
silica gel: dehydration of gases
activated alumina (aluminum oxides): dehydration
molecular sieve (synthetic zeolites): SO-, No „ Hg
5.30
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5.40
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CHAPTER- 6
SECTION II
MOLECULAR SEPARATION
6.1 INTRODUCTION
The following chapter examines the "Recycle, Recovery, and Reuse
Applications" of several ciolecular separations processes. The proceiisas
included in this chapter are:
1. Reverse Osmosis
2. Ion Exchange
3. Ultirafiltration
Ultrafiltration and Reverse Osmosis are commonly referred to as membrane
processes. A membrane is defined as a phase which acts as a barrier to flow
of molecular or ionic species between other phases that it separates. On the
other hand, Ion Exchange can be considered a sorption process (Sundstrom and
Klei, 1979). In Ion Exchange, there is a reversible interchange of ions
between a liquid and sclid (the transfer of ions between phases occurs at the
solid suriace) where there are no permanent changes in the structure of the
solid.
Chapter 6 is divided into two major sections. The first section of the
chapter will examine the recycle, recovery, and reuse applications for or-
ganic compounds as related to the two membrane processes listed above. The
second section of the chapter will then examine the recycle, recovery, and
reuse applications for inorganic compounds as related to the ion exchange and
reverse osmosis processes.
6.2 ORGANIC COMPOUNDS
6.2.1 Membrane Processes
6.1
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Membrane ultrafiltration and reverse osmosis are hydraulic pressure
activated processes capable of separating solution components largely on the
basis oi molecular size and shape, and involve neither a phase change nor
interphase mass transfer. By proper membrane selection, it is possible to
concentrate, purify, and fractionate many components of a solution. These
processes are particularly attractive due to the fact that the sole energy
requirement is the compression energy of the feed liquid.
Reverse osmosis generally applies to the separation of low-molecular
weight solutes such as salts, sugars, and simple acids from their solvent.
The driving pressure for efficient separation must exceed the osmotic pres-
sure of the solute in solution. This may require pressures of 500 to 2,000
psi. Ultrafiltration is the term used for separation of higher molecular
weight solutes such as proteins, starch, natural gums, and other complex
organic compounds, as well as colloidally dispersed substances such as clays,
pigments, minerals, latex particles, and raicroorgaEisms, from their solvents.
Osmotic pressure of the solute in these systems is usually negligible, and
typical operating pressures range between 5 and 100 psi. Although the pro-
cesses are related, ultrafiltration does not require the high operating
pressures which are needed to overcome the high osmotic pressure differential
across a reverse osmosis membrane (Porter, 1972). Both systems, however, are
worth consideration in treating many streams to produce a concentrate suit-
able for reuse.
6.2.1.1 Membrane Characteristics
The membranes for both ultrafiltration (U.F.) and reverse osmosis (R.O.)
can be made from various synthetic or natural polymeric materials, ranging
from hydrophilic polymers such as cellulose, to hydrophobic materials such as
6.2
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fluorinated polymers. Polysrylsulfonates and inorganic materials have also
been introduced to deal with high temperatures and pll needs (Bcrkonitz, et_
al. 1976).
The use of cellulose acetate membranes or their derivatives imposes some
limitations. Operating temperatures must be restricted to less than 110CF to
avoid hydrolysis of the cellulose acetate. Cellulose acetate membranes
normally are limited to operating within the pll range of 3 to 8. Strongly
acid or alkaline solutions will cause rapid membrane degradation (Ruver,
1973). Certain noncellulosic membranes have temperature capability of 230 F
and pH capability between 1 and 12 (Porter, 1972).
Membranes having an anisotropic structure, with poses roughly conical in
shape are not subject to internal fouling problems. The smallest pore
diameter remains at the membrane surface. A solute which finds its way into
the membrane is likely to pass through to the other side of the membrane,
since pore diameter increases from entrance to exit (Porter, 1973).
Ohya, et al. (1979) studied the effect oT evaporation period at casting
stage on the water flux and membrane structure of a cellulose acetate buty-
i
rate membrane. With short evaporation time, membranes with large fingerlike
cavities were formed. No holes were formed on the upper surface. Water
flux properties were low. Upon long evaporation periods, a solid structure
I
was formed. These membranes tended to have high flux properties. No explana-
tion was offered for the relationship between membrane structure and its
characteristics.
6.2.1.2 Membrane Rejection and Flux
According to Spatz (1973), the rejection of organics is based on a sieve
mechanism related to the size and shape of the organic molecule. In the case
6.3
-------
of organicr, which act like salts, a combination of rejection mechanisms may
occur, since salts are rejected because of the physiochemical reaction with
the membrane surface.
Sourirajan and his coworkers have studied organic separation by cellulose
acetate membranes, and found solute separation to be dependent on its ability
to form hydrogen bonding with the membrane materials (Chian and rang, 1977).
Chian and Fang attempted to establish generalized criteria conducted
with five membrane types and dozens of organic compounds, and found that the
physio-chemical criteria and pressure effects on solute separation established
with the cellulose acetate membrane are generally valid with other commercial-
ly feasible membranes. For instance, for membranes having appropriate surface
structure, pore size, etc.» the more nonpolar the membrane, the better the
solute separation will be, particularly for low molecular weight polar
organic solutes. The choice of nonpolar membrane materials, however, may
produce a decrease in water flux (Chian and Fang, 1977).
Once a membrane is selected which provides the desired removal of
solute, the remaining important operating parameter is membrane permeability
or flux. Initially, membrane resistance controls flux. However, when the
solute begins to build up along the membrane surface, a polarized layer, or
gel forms. When the gel concentration exceeds a critical level, gel resis-
tance controls mass transfer (Nelson, 1973).
In the presence of large surfactant concentrations, almost instantaneous
fouling can take place, a condition to which only low surface energy polymers
are immune. Fouling can be controlled to a high degree by high circulation
velocities, proper membrane configuration, and control of process fluid
composition (Mir. j2£ al.. 1977).
6.4
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Fenton-May and his coworkers (Fenton-Kay, et al. 1972) found *:hat at low
flow rates, the primary resistance to membrane transport is offered by a
hydrodynamic boundary layer produced by polarization, and that mass transfer
is controlled by membrane resistance and gel precipitate at higher flow
rates.
For both reverse osmosis and ultrafiltration, Fenton-May osmosis and his
coworkers found an increase in permeate flux of 40% for every 20°F increase
in feed temperature.
In studying pressure effects, they found a completely linear relationship
between applied hydrostatic pressure and membrane pure water flux up to a
pressure of about 450 psi, indicating that, within this range, resistance of
the membrane itself to mass transport is pressure independent. When a whey
or skim milk feed was used, however, an increase in operating pressure in-
creased solute rejection, a result of an increase in resistance to solute
transport of the protein gel layer.
Since membrane flux rates are for the most part limited by concentration
polarization or gel resistance, various techniques have been applied to
reduce this problem, generally by cross-flow fluid management techniques. It
has been reported that by operating above a critical cross-flow velocity, gel
resistance is minimized and flux increased with increasing pressure. An
economic optimum must be reached between power costs necessary to maintain
the desired cross-flow velocity and shear effects and membrane area costs
determined by membrane flux.
6.2.1.3 Prediction of Binary-Solute Behavior
Fels (1972) studied the permeation and separation of binary organic
mixtures using polyethylene membranes, and found that ideal behavior was not
6.5
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exhibited. The deviation from ideal behavior increased as the difference in
interaction behavior between the liquids anc1 the polymer (as measured by a
solubility parameter difference) increased. The purpose of this study was to
contribute to the ideal of predicting separation behavior of membranes from a
knowledge cf the individual component behavior of the systera. 6.2.1.4
6.2.1.4 Statement of Limiting Technology
1. Membrane Characteristics
The relationship between membrane structures
and their rejection and flux properties are
not fully understood.
A need exists for better membranes which will
have longer life under the varying operating
conditions of temperature, pressure, pH, and
flow rate and which are less prone to fouling
and chemical degradation, have higher water
olux rates, and good solute rejection charac-
teristics.
i
2. Membrane Rejection and Flux
The membrane properties of flux and rejection
rarely control process performance. Perfor-
mance is usually limited by concentration
polarization or gel formation at the membrane
surface, and is less efficient than membrane
controlled performance. The answer to the
problem may be found in the study of one of
three areas: improved hydrodynamics result-
6.5
-------
ing in higher shear forces; the interaction of
gel layers, or dynamic membranes; with the
membrane, or the interaction between the
membrane polymer and feed.
Little is knoun about the possibility of
reducing the influence of undesirable dynamic
membranes formed from feed constituents.
It may be possible to purposely add species
capable of forming gel layers, or secondary
membranes, which may enhance membrane processes,
to the feed.
6.2.1.5 Resource, Recovery, and Reuse Applications
Production of protein concentrates and isolates from
soy whey.
. Concentration and fractionation of cheese whey and
skim milk.
. Oil-emulsion concentration.
. Polyvinyl alcohol recovery and concentration.
Recovery of protein and pectin from sugar beet
wastes.
Recovery of lignin and ligno-sulfonates from
pulp and paper extraction effluent.
Recovery of polyglycols from polyurethane
production processes.
Recovery of chocolate wastes.
6.7
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6.3 INORGANIC COMPOUNDS
This section of Chapter 6 examines the recycle, recovery, and reuse
applications for organic compounds as related to the ion exchange and reverse
osmosis processes. 6.3.1
6.3.1 Ion Exchange
Ion exchange is a process in which ions held by electrostatic forces to
charged functional groups on the surface of a solid are exchanged for ions of
similar charge in a solution in which the solid is immersed (Weber, 1972).
Basically in this process, the ion exchanger is contacted with the solution
containing the ion to be removed until the active sites in the exchanger are
partially or completely "exhausted" by that ion. The exchanger nay then be
contacted with a sufficiently concentrated solution of the ion originally
associated with it to "regenerate" it back to its original forme
The exchange reactions during "exhaustion" and "regeneration" can be
represented by the following two reactions:
Exhaustion: M+X~ + R~X+ £ R~H+ + N* -r X~ (6.1)
Regeneration: R~M + N (high concentration)
•> R~N+ + H+ (6.2)
In the first reaction, a cation exchange material designated g. , having a
+ + —
cation N associated with it reacts with a solution of an electrolyte (11 X ).
In the regeneration reaction concentration of N is higher than in the ex-
haustion reaction and the solution volume for regeneration ia smaller, there-
by making concentration of M higher in the regeneration solution.
Regeneration of ion exchanger may also involve a third ion (for example
a hydrogen ion in cation exchange) to give the corresponding form of the
exchanger which can then be converted to the desired salt as shown below:
6.8
-------
R~M+ + H+ -*• R~K'*" + M+ (6,3)
R~H+ + N+OH~ -*• R~N+ + H20 (6.4)
Such a sequence might be desirable in a case where H was a much more
effective regenerant than N but where the release of H+ into the solution
being purified will be undesirable (Arthur D. Little, Inc., 1976).
Thus, during the process of ion exchange, undesirable ions from a stream
are removed and transferred at a higher concentration to another aqueous
stream.
The phenomenon of ion-exchange is known to occur with a number of natural
solids (for example, soil, humus, metallic oxides, etc.) as well as synthetic
resins which are presently used for most ion exchange applications.
6.3.1.1 Types of Ion Exchange Operations
Ion exchange operations are basically batch type but may be used on a
semi-continuous basis. There are four operations carried out in a complete
cycle, namely, service (exhaustion), backwash, regeneration, and rinse. There
are three principal operating models in use today: concurrent fixed-bed,
counter-current fixed bed, and continuous counter-current. Most ion exchange
i
installations in use today are of the fixed bed type with counter-current
operation becoming more popular, especially for reicoval of traces of hazardous
species from the waste stream prior to,reuse or discharge (Arthur D. Little,
Inc., 1976).
6.3.1.2 Ion Exchange: State of the Art
One of the applications of the ion exchange process is in the Betal-
finishing industry for the recovery of chromic acid. The acidity of a chrome
bath of average use is so high (pH 0.5 or less) that the use of any presently
knovn cation exchange resin for direct rercoval of cations is impossible.
6.9
-------
Also, the high oxidatlve potential of the waste results In rapid resin degra-
dation of almost all available cation exchange resins (Raman and Carlson,
1977).
In a typical chromic acid recovery system, the acid rinse stream is
first neutralized to a pH 8-9. Chromium (VI) is then removed by contact with
a strong base ion exchanger (hydroxide form) and the resin is regenerated
with a sodium hydroxide solution. The spent regeneration solution, which
contains sodium chromate and sodium hydroxide, is neutralized with sulfuric
acid and then treated with a cation exchanger to give chromic acLd for
recycle to the plating baths (Arthur D. Little, Inc., 1976). Hall, e£ .al.
(1979) quotes a study in which a chromic acid recovery efficiency of 99.5%
has been demonstrated. Reduction in chromic acid purchases of 76-90% was
also reported. Nitric acid can be recovered in a similar manner.
Recovery of valuable metals such as chromium, nickel, silver, and gold by
ion exchange is more economically attractive than the conventional waste
treatment processes (Fisher and McGarvey, 1967). A survey conducted by
Plating and Surface Finishing journal (Anonymous, 1979) showed a favorable
pay back for recovering nickel and gold with ion exchange equipment. It was
reported that equipment cost payback of the chromium recovery units was not
favorable because the equipment was old and not representative of current
design for cjsximum. efficiency.
Ic/n exchange is more attractive economically for the removal of heavy
metals than the lighter ones when based on a weight basis, since the capacity
of an Ion exchanger is based on equivalent weight. For example, the weight
of silver is 107 and of sodium 23, so that an exchanger can pick up four
times the weight of silver compared to the weight of sodium it can hold (Gold
6.10
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and Calmon, 1980).
Another large scale application of the ion exchange process iu the
removal of aluminum from strong phosphoric acid/nitric acid solution used for
cleaning ("bright dipping") aluminum metal (Skovronek and Stinson, 1977).
The contaminated phosphoric acid is diluted with rinse tank water to give a
40% phosphoric acid solution which is then subjected to acid exchange to
remove the aluminum. The purified phosphoric/nitric acid mixture is then
evaporated to produce concentrated acid for recycle to the process. The
resin is regenerated with sulfuric acid to give aluminum sulfate.
The ion .exchange technique can be improved in terms of its utility and
economics by using some ingenuity in design. For example, an ion exchange
system, called "Reciprocating Flow Ion Exchange" has been perfected by Eco-
Tec Limited for recovery of waste metals from plating operations (Brown,
1975).
There are a number of new developments in the areas of metal pickling
waste treatment, cyanide removal, and novel ion exchange resins. A number of
new ion exchange reslas are being tested on a laboratory and pilot scale (Gold
and Calmon, 1980). Many of these resins are of the macroreticular type and
are less subject to fouling and loss of capacity than the older saterials.
6.3.1.3 Limiting Technology
The ion exchange process is a well established process used in various
industrial operations, however, the major limiting fa ' T in applying this
technique to new situations seems to be the presence of materials or condi-
tions which may clog, attack, or foul the resins. For example, high concen-
trations of oxidizing agents such as nitric acid can damage the resins.
Active research is currently being conducted to evaluate the use of new ion
exchange materials, which would not be affected by the presence of such
6.11
-------
materials as mentioned above.
There seems to be a need for the development of highly basic anion
exchangers which are stable at elevated temperatures when in the base form.
Highly basic anion exchangers tend to foul with sonic surface waters and in
solutions containing high molecular anionic species, therefore atonic
exchangers less subject to fouling are needed which would increase applica-
tions in solutions containing foulants (Gold and Calmon, 1980).
More research is warranted to develop continuous ion exchange systems
requiring less technical supervision and BIOTP controllability than those
which exist.
In some cases the regenerant or eluting solution is not economically
worth recovering or reusing. It can however become a pollutant if discarded
into sewer lines or receiving waters. Therefore, more research is needed on
full utilization of regenerants, higher regenerant efficiency, and reuse of
regenerant effluents containing umised regenerant.
i
6.3.1.4 Recycle, Recovery, and Reuse Applications
The ion exchange process has been used for several years by different
i
industries. Ion exchange is currently used for both general and selective
removal of primarily inorganic ion species. Applications of ion exchange
process in the waste treatment area include: treatment of a wide variety of
i
dilute wastewaters from electroplating and other metal finishing operations,
recovery of materials from the fertilizer manufacturing industry and hydro-
metallurgical processes, removal of cyanide from mixed waste streams, and
recovery of chromium from cooling tower blowdown.
6.3.2 Reverse Osmosis
Osmosis is defined as the spontaneous transport of a solvent from a
6,12
-------
dilute solution to a concentrated solution across an ideal sewipermeable
membrane, which impedes passage of solute but allows solvent flow (Weber,
1972). At a certain pressure exerted on the solution side 01 the membrane,
called osmotic pressure, equilibrium is reached and the amount of solvent
which passes in each direction is equal. If the pressure is increased above
the osmotic pressure on the solution side of the membrane, the flow reverses.
Pure solvent will then paes from the concentrated solution to the dilute
solution. This Is the underlying principle of the reverse osmosis,
2
The solvent flux (frequently expressed in gallons/ft -day) is given by
(Arthur D. Little, Inc., 1976):
J - K (AP)7i (6.5)
In which AP is the applied pressure, the osmotic pressure end K is a
constant for the membrane-solvent system. As can be seen from this equation,
the pro-Juct-water flux rate decreases with increasing salinity (increasing
•
osmotic pressure) of the feed solution.
The basic components of a reverse osmosis unit are the membrane, a
membrane support structure, a containing vessel, and & high-pressure pump.
Cellulose acetate and nylon are more common among the membrane materials
used. The chemical nature of the membrane material is Important because It
affects the transport of solvent and rejection of solute. The membranes are
susceptible to cheaical attack and fouling and so pretreatmer.t of certain
feedwaters may be necessary to remove oxidizing materials. Usually, as a
part of pretreattsent, iron and manganese salts are removed to decrease pealing
potential and the pH is adjusted to a range of 4.0 to 7.5 to inhibit scale
formation.
6.13
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6.3.2.1 Process Configurations
Based on the membrane support structure, reverse osmosis units may be
classified under four categories: spiral-wound, tubular, plate and frame, and
hollow fiber. The tubular configuration is recommended for use with domestic
wastewater effluents while reverse osmosis system using a multitude of hollow
nylon or poiyamide fibers have shown considerable utility on commercial waste
streams. Reverse osmosis units can be arranged either in parallel to provide
adequate hydraulic capacity or in series to effect the defined degree of
demineralization.
6.3.2.2 Reverse Osmosis: State of the Art
Research in the area of reverse osmosis has recently focused upon the
development of improved families of membranes with increased flux, greater
resistance to degradation in various liquid environments and improved rejec-
tion characteristics. Progress is also being made In recent years in impro-
ving mechanical designs for the modules, which can work efficiently with thin
membranes at operating pressures of up to 800 psig (Leitner, 1973).
The effect of pH and temperature or membrane permeability was studied by
Beder and Gillespie (1970). They reported that the flux rate was slightly
higher under alkaline conditions. Their results also showed that & 5°C de-
viation from 25°C produced a 15% change In the membrane permeability constant,,
K. Similar results were reported by'Wiley, e£ al_. (1967).
Kojima and Tatsutni (1977), who studied the reverse osmosis treatment of
wastewater from a chemical plant, reported that the performance of the mam-
brance deteriorated gradually due to fouling and compaction of the membrane.
It was found that the presence of organic matter, silica, calcium, and iron
in the feed was responsible for the damage of the membrane. Pretreattnent of
6.14
-------
the feed to reverse osmosis units is necessary for njmost all industrial
wastewaters. Due to the sensitivity of the membranes to the high concentra-
tions of suspended solids in wastewstcrs, diatomaceous filters followed by a
sand filter (Warnke, _ejt al_. 1976). or coagulation and .sedimentation (Kojiraa
and Tatsumi, 1977), have been used for precreatment purposes. Removal of
high concentrations of suspended solids in the feed before reverse osmosis is
necessary in order to prevent clogging of the membrane and subsequent
decrease in flux rates. Fouling of the membrane due to the presence of
certain chemicals can be overcome by precipitating and filtering such
materials by chemical treatment (Zabban and Helwick, 1980).
6.3.2.3 Statement of Limiting Technology
Reverse osmosis is a relatively new process and the development of this
process has accelerated within the past few years, with a substantial, increase
in the number of commercial installations. There are, however, certain
practical limitations to the use of reverse osmosis for waste recovery and
reuse.
There seems to be a limitation on the pressures used in the reverse
osmosis process. At high pressures, the membranes are subjected to compac-
tion, which is accompanied by a decrease in product flux. Most units are
limited to moderate temperature, acidic pH, and influent uhich can be pre-
filtered effectively to prevent fouling of membranes (Hall, et^ ajL. 1979).
The membranes available in the market at the present time are not
sufficiently resistant to a wide range of chemicals, such as is often found
in waste streams. These membranes do not seem to withstand extreme pH,
temperature, and pressure. More research is needed to develop new membranes
which will broaden the application of reverse osmosis.
6.15
-------
Due to the limited applicability of the membranes, most of the indus-
trial waste streams need some type of pretreatraent prior to entering the
reverse osmosis unit. Such pretreatment would, obviously, add to the overall
cost of the treatment system and might pose a limitation to the use of
reverse osmosis.
The waste stream from the reverse osmosis operation, in some cases, must
be concentrated in an evaporator or subjected to some other treatment for a
complete recovery of the pollutants. The limitations of reverse osmosis
systems used in various industrial waste treatment operations are summarized
in Table 1.
TABLE 6.1 EVALUATION OF RO FOR SYSTEMS TESTED (SKOVRONEK AND STINSON, 1977)
Attractive Systems Limitations
Watts-Type Nickel Boric acid selectively
permeates membranes
Nickel Sulfamate boric acid selectively
permeates membranes
Copper Pyrophosphate Possible- decomposition of
pyrophosphate
Nickel Fluoborate Boric acid selectively
permeates membranes
Zinc Chloride Need evaporation to close
loop
Copper Cyanide Need low-pH bath for current
membranes:
Zinc Cyanide Need low-pH bath for current
membranes: need evaporation
to close loop
Cadmium Cyanide Need low-pH bath for current
membranes: need evaporation
to close loop
Unattractive Systems Limitations
Chromic Acid Attacks and destroys all
membranes unless neutralized
Very-high pH Cyanide Attacks and destroys all
Baths membranes commercially available:
newer membranes under development
shov; promise for treating high-pH
cyanide baths
6.16
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6.3.2.4 Recycle, Recovery, ar.d Reuse Applications
Reverse osmosis is gaining importance as an industrial unit operation
only in recent years. Initially, it was used for production of potable
water, however, it is currently used in a broad spectrum of industrial
operations. Recent research indicates wastewater reclamation by reverse
osmosis offers great promise for substantial reductions in cost as well as
marked improvements in pollutant removal efficiency.
Reverse osmosis has been used for various industrial operations and its
use is expected to expand as its utility is demonstrated and its technology
becomes more familiar to its potential users. Some of the applications of
reverse osmosis in waste treatment area include: plating wastes, paper mill
effluents, laundry wastewaters, food processing wastes, acid mine drainage
waters, and petrochemical wastewaters.
6.17
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BIBLIOGRAPHY
Anonymous.. "Recovery Pays." Platinp, and Surface Finishing;,
662, 4548, 1979. ~"
Arthur D. Little, Inc., Physical, Chemical and Biological
Treatment Techniques _l_n Industrial Wastes, Vol. 11. ~
National Technical Information Service!PU275 287, 1976.
Beder, H. and Gillespic, W.J. "Removal of Solutes from
Mill Effluents by Reverse Osmosis." Tappi, 53, 5, 883-887, 1970.
Berkonitz, J.B. ejt a_l. Physical, Chemical, and Biological
Treatment Techniques for Industrial Wastes. NTIS
No. PB275054, Arthur D. Little, Inc.7~Cambridge, Mass.,
1976.
Brown, C. "Effective Nickel Recovery Will Prove Profitable."
Plant Management and Engineering, 34, 8, 2729, 39, 1975.
Chian, E.S., and Fang, H.H. "Physicochemical Criteria
Removal." AICHE Symp. Series. No. 166, Vol. 73,
p. 152, 1977.
Cruver, J.E. "Reverse Osmosis for Water Reuse." AICHE Conf.
on Complete Waterguse, p. 619, 1973.
Fels, A. "Permeation and Separation Behavior of Binary
Organic Mixtures in Polyethylene." AICHE Syrop. Series,
No. 120, Vol. 68, p. 49, 1972.
Fenton-Hay, R,I., Hill, C.G., Araundson, C.H., and Auclair, P.O.,
"The Use of Pressure Driven Membrane Processes in the
Dairy Industry." AICHE Sytnp. Series, No. 120, Vol. 68,
p. 31, 1972.
Gold, H. and Caltnon, C. "Ion Exchange: Present Status,
Needs, and Trends. In: Recent Advances In Separation
Techniques." AICHE Symp. Series, No. 192, Vol. 76,
p. 60-67, 1980.
Hall, E.P., Lizdas, D.J., and Auerbach, E.E. "Recovery
Techniques in Electroplating." Plating and Surface
Finishing, 66, 2, 49-53, 1979.
Kojima, Y. and Tatsurai, M. "Operation of Reverse Osmosis
Process for Industrial Waste Water Reclamation."
Desalination, 23, 8795, 1977.
Leitner, G.F. "Reverse Osmosis for Water P>ecovery and
Reuse." Chemical Engineering Progress^ 69, 6, 83-85,
1973.
6.18
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Mir, L., Eykanp, W. and Goldsmith, R.L. "Current and
Developing Application:* for Ulcraf il t rat ion. " Ind .
Water Eng. 14(3):14, May/June, 1977.
Nelson, R.F. "Ultraf iltration for Polyglycol Removal."
AICHE Conf . on Complete Watcrcuse, p. 926, 1973.
Ohya, H., Akinoto, N., and Negishl, Y. "Reverse Osraosiy
Characteristics of Cellulose Acetate Butyrate
Membranes." ^. Applied Polymer Science, 24 (3): 663,
1 Aug., 1979.
Porter, M.C. "Ultrafiltration of Colloidal Suspensions."
AICHE Symp. Series. No. 120, Vol. 68, p. 21, 1972.
Raman, R. and Karlson, E.L. "Reclamation of Chromic Acid
Using Continuous Ton Exchange." Plating and Surface
Finishing. 64, 6, 40 and 42, 1977.
Skovronek, H.S. and Stinson, M.K. "Advanced Treatment
Approaches for Metal Finishing Wastewaters: Part 2."
Plating and Surface Finishing, 64, 11, 24-31, 1977.
Sunds:ro3i, D.W. and Klei, H.E. Wastevater Treatment.
Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1979.
Warnke, J.E. , Thomas, K,G. , and Creason, S.C. "Reclaiming
Plating Wastewater by Reverse Osmosis.'1 Proc. 31st
Industrial Waste Conference, Ann Arbor Science Publishers,
Inc., Ann Arbor, Michigan, pp. 525-530, 1976.
Weber, W.J., Jr. Physicoc'ncmical Processes For Water
Quality Control. Hiley-Interscience, New York, New York,
1972.
Wiley, A.J., Ammerlain, A.C.F. , and Dubey, G.A. Tjjpjrl. 50,
9, 455, 1967.
Zabban, W. and Helwick, R. "Cyanide Waste Treatment
Technology-The Old, The New, and The Practical."
Plating and Surface Finishing, 67, 8, 56-59, 1980.
6.19
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SUPPLEMENTAL REFERENCES
Bailey, P.A. "Ultrafiltration - The Current State of the
Art." Filtration and Separation. Vol. 14(3):213,
May/June, 1977.
Brandon, C.A. and Samfield, M. "Application of lligii-
Tereperature Hyperfiltration to Unit Textile Processes
for Direct Recycle." Desalination. 24(1/2/3) :'J7,
Jan. 1978.
Goldsmith, R.L. , de Fillppi, R.P., and Hossain, S. "New
Membrane Process Applications." AICHE Syrep. Series,
No. 120, Vol. 68, p. 'I, 1972.
Gross, M.C., Markind, J, and Stana, R.K. "Membrane
Experience in Food Processing." AICHE gyrojv^ Series,
No. 129, Vol. 69, p. 81, 1973.
Masuda, H., Kamyawi5 C., Hata, K., Yokota, K., Sakai, T.
and Soto, M. "Concentration of Acetic Acid in Sulfite
Pulp Evaporation Drain by Reverse Osraosis." Desalination
25(1):89, Mar. 1978.
Murkes, "Some Viewpoints on the Industrial Application of
Membrane Technology." Desalination 24(1/2/3):225,
Jan. 1978.
Spatz, D.D. "Reclamation and Reuse: of Waste Products froia
Food Processing by Membrane Processes." AICHE Syrap.
Series. No. 129, Vol. 69, p. 89, 1973.
6.20
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CHAPTER 7
SECTION II
PHASE TRANSITION
7.1 INTRODUCTION
Processes of heat transfer accompanied by phase changes are more complex
than simple heat exchange between fluids. A phase change involves the addi-
tion or subtraction of considerable quantities of thermal energy at constant
or nearly constant temperature. In Chapter 7, four processes will be examined
vhich rely on one (or several) constituents of a wastestream to undergo a
phase change in order to separate it (and in many cases these constituents
are recycled and reused) from the main fluid stream. The processes to be
examined include:
1. Condensation
2. Distillation
3. Evaporation
4. Refrigeration
Condensation, evaporation and refrigeration are processes used primarily
to separate the constituents of a wastestream. Once separated, these consti-
tuents can be further purified and either recycled back into the process or
sold. Evaporation, on the other hand, is basically used to concentrate a
non-volatile solute by vaporizing the volatile solvent. The solvent, can
then be condensed, purified and recycled into the process for further use.
The concentrate (non-volatile solute and remaining solvent) can also be
recycled or disposed of at this point.
For each of the four listed processes, a brief process description will
be provided. Also, a review of the current recycle, recovery, and reuse
7.1
-------
applications will be given as well as a statement on the processes limiting
technology.
7.2 COOTF.NSATION
In a two conponent vapor containing one condensable and one noncondens-
able component, condensation will occur whon the partial pressure of the
condensable component equals that conponent's vapor pressure. This may be
effected in one of two ways: The system pressure may be increased at a given
temperature until the partial pressure of the condensable component equals
its vapor pressure. Alternately, and far more commonly, the pressure remains
fixed and the temperature of the mixture is reduced to the point where the
vapor pressure of the condensible component equals its partial pressure* At
further reduction in temperature, condensation continues such that the partial
pressure is always equal to the vapor pressure (Anonymous, 1978).
Condensers may employ contact or non-contact methods for cooling the
vapor. .Contact condensers usually spray an ambient temperature or slightly
chilled water or other liquid directly into the gas stream in order to
condense the vapor. The contact condenser may also act as an absorptive
system, scrubbing vapors which might not be condensed, but which are soluble
in the liquid. Because the temperature approach between the liquid and the
vapor is very small, condenser efficiency Is high. Large volumes of liquids
are required, however.
Direct contact condensers are seldom used for the removal of organic
solvent vapors because the condensate will contain an organic-water mixture
which must be separated or treated before disposal. They are effective in
cases whore it is necessary to remove heat from hot gas streams without
concern for recovery of organics. Spray towers, high velocity jetst and
barometric condensers are among the equipment used for contact condensation.
7.2
-------
In practice, crude empirical correlations are usiuilly used in designing and
predicting performance of a contact unit (Theodore, and Buonicore, 1975).
Surface condensers are non-contact units which may also be referred to
as heat exchangers. A common surface condenser is the shell-and tube heat
exchanger in which the coolant flows through the tubes and vapor condenses
on the outer tube surface. The film of condensed vapor which develops
drains away to storage or disposal. In this way, the coolant contacts
neither the vapor nor the condensate. Surface condensers may also be air-
cooled. These air-cocled units usually have extended surface fins; vapor
condenses within the finned tubes (Theodore and Buonicore, 1978).
Although contact condensers are generally less expensive, easier to
maintain, more flexible, and more efficient in removing organic vapors than
surface condensers, surface condensers are more attractive with respect to
recovery of marketable coridensate and a minimal waste disposal problem
(Anonymous, 1978). Furthermore, watei' used as a surface condenser coolant
may be reused, and surface condensers produce 10 to 20 times less condensate
than do contact condensers (Theodore and Buonicore, 1978). Because high
i
removal efficiencies are not obtainable with low condensable vapor concentra-
tions, condensers are typically used when the vapor concentration in the
strean to be treated is high, and are often located upstream of after burners,
carbon beds, or absorbers as a pretr^atment measure.
7.2.1 Limiting Technology
High removal efficiencies are not obtainable with low concentrations of
condensable vapors. This limits the application of the condensation process
to streams having a high vapor concentration or to pretreatment of streams
fed to after burners, carbon beds or absorbers.
7.3
-------
A shell and tube heat exchanger installed on a neoprene Konosicr isomcri-
zation tower was installed to treat a total waste gas flow of 331 Ib/hr. Tbe
hydrocarbon waste gas flow was 159 Ib/hr. The exchanger, cooled by -2°F
brine solution, condensed 81% of Che contained hydrocarbon uith an energy
requireEont of 22,000 Btu/hr. The recovered hydrocarbons were returned to
the process for utilization (Pruessner and Broz, 1977).
In a process in which fuels are produced from coal, volatile products
released from the coal in fluidiued bed reactors pass to a product recovery
system for recovering the oil and cooling the gases. The coal-oil vapors are
directly contacted with a water-rich streaia for condensation. The oil-phase
is dehydrated and filtered to remove solids before being pumped up to pressure
and mixed with hydrogen for hydrotreating in a fixed-bed catalytic reactor.
Hydrotreating removes sulfur, nitrogen, and oxygen to produce a synthetic
crude oil (Jones, 1974).
Power plant turbine exhaust steam has been mixed with cooling water in
a direct contact condenser maintained under a vacuum. The temperature of
the water is less than the boiling temperature under the vacuum conditions
in the condenser. The mixture of cooling water and condensed turbine exhaust
is divided such that one portion is sent to the boiler, suitable for use in
generating steam to drive the turbine, while the other portion is seat to the
condenser for use as cooling water after it has passed through an air cooled
heat exchanger. Water to be used for cooling is placed in the heat exchanger
with liquid gaseous fuel so that the fuel ia vaporized at the expense of heat
lost from the water (Anonymous, 1974).
In work on liquid fuel synthesis using nuclear power in a nobile energy
system, Steinberg and Seller proposed to extract CO, from the atmosphere by
7.4
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compressing air, condensing the w.itc-r front it, drying r.lie resultant air with
a molecular sieve, and extracting CO- by another molecular sieve (Steinberg
and Seller, 1964). Williams and Campagne (1971), however, found compressor
costs for such an operation to be prohibitive.
At a neoprene polyner plant where neoprone latex is manuf(• ctured in
batch reactors, each charging and emptying of a polymerization reactor
causes displacement of some waste gas. Collected waste gas is discharged to
a direct contact cooler. A problem which precluded the use of a shell
and tube exchanger was the regular carryover of latex to the collection
system, anticipated to produce a high rate of fouling. The waste gas flow of
275 Ib/hr, containing about 125 Ib/hr hydrocarbon contamination, is cooled
with chilled water resulting in the condensation of 43% of the hydrocarbon.
Exit gas from the direct contact cooler is treated in an absorption system
The absorption systeta consists of a five-stage oil absorption tower. An
overall efficiency of the contact cooler/absorption system exceeds 98%
hydrocarbon removal. The recovered hydrocarbon is stripped from the oil and
returned to the manufacturing process for further use. The installed cost of
the system amounted to §300 (Pruessner and Broz, 1977).
A solvent recovery system features an inert nitrogen atmosphere in an
oven/dryer process. In this process, resin curing is accomplished by evapora-
ting the organic solvent in which the resin is dissolved. This eliminates
the requirement for oven ventilation with atmospheric air normally required
to dilute solvent concentrations to b«lou-explosive levels. By using thp
inert nitrogen atmosphere, solvent vapor can be safely concentrated to well
above traditional oven levels. At these levels, the solvent is recoverable
by condensation. According to the manufacturer, solvent recovery is about
99%, and overall fuel requirements arc reduced by 40% (Anonymous, 1980).
7.5
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ILLrtl 1U[>
Distillation is a unit operation employed by Industry for the separation,
segregation, or purification of liquid organic product streams, some of which
nay contain aqueous fractions. The term distillation is properly applied only
to those operations in which vaporization of a liquid mixture yields a vapor
phase containing more than one component. This distinguishes the process from
that of evaporation.
As a unit operation, distillation has been successfully used either
singly or in combination with such operations as direct condensation, adsorp-
tion, and absorption for the recovery of organic solvents. With regulations
which are becoming increasingly stringent for air pollution control, liquid
effluents, land site disposal, and the rising cost of organic chemicals,
distillation should become more competitive with other methods of organic
liquid recovery and disposal.
The practical limitations of the process are economic in nature; both
operational and equipment costs are high. The difficulty in .separating the
contents in the liquid to be distillel) defines the economic and energy
requirements of the process (Berkowitz, ct^ a^L. 1976).
Theoreticallys distillation can< generate products of 100% purity.
i
Physical parameter restrictions such as entrainment effects limit the
-9 -14
degree of attainable purity to the 10 to 10 rfinge of impurities, however.
Usually, the attainment of these limits is not necessary.
In terms of the physical separation of liquid components, there are no
limitations in feed composition or in reaching the desired composition in
any of the product streams. To avoid plugging of equipment or cost3.y mainte-
nance problems, however, it is preferred that the materials to be distilled
7.6
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do not contain appreciable quantities of solids or non-volatile materials,
and that the feed docs not have a tendency to polymerize. If it iu known that
feeds of a "dirty" nature must be handled, prutreatment steps employing
filtration, thin-film evaporation, ocrubbers, electrostatic precipit.itore, cr
cyclones may be taken. When pretreatment is not possible, specially designed
equipment may be required.
7.3.1 Types of Distillation Processes
The most common types of distillation are those of batch and continuous
fractional distillation. Certain feed streams require more specialized
processing, however.
When it is necessary to distill an aseotrope, pressure or vacuum may be
applied to shift the azeotropic composition. More often, an additive is
introduced to the ti.ixture to form a new boiling point azeotrope with one of
the original constituents. The volatility of the new azeotrope is such that
It may be easily separated from other original constituents.
Binary mixtures which are difficult or impossible to separate may also
be distilled by extractive distillation. In this process, a solvent is added
to the mixture which alters the relative volatility of the original consti-
tuents, thus permitting separation. The added solvent is of low volatility
and not appreciably vaporized.
In the case of a heat sensitive feed stream, colecular distillation nay
be used. This process is conducted at absolute pressures on the order of
0.003 mm of mercury (Berkowitz, et. al. 1976).
7.3.2 Limiting Technology
Theoretically, distillation can generate products of absolute purity.
—9 —14
Entrainment effects limit the degree of attainable purity to the 10 to 10
7.7
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range. This level of purity is rarely required.
The presence of formation of solids or non-volatile material in the feed
stream is undesirable due to operating difficulties which they may cause. In
caeeL where such materials are present, pretreatment steps such as filtration
are ^ncessary to minimize the plugging of distillation equipment or coctly
maintenance problems.
In some distillations, solvents may be added which alter the volatility
of a binary mixture which is difficult to separate. Further study of addi-
tives which produce this beneficial effect may be useful.
The fact that the distillation process is energy intensive tends to
limit its application, but with increases in by-product recovery credits, it
may become competitive with more conimonly utilized processes.
Organic peroxides, pyrophoric erganics, and inorganic wasters cannot
generally be treated by distillation.
7.3.3 Recycle, Recovery, and Revise Applications
Typical industrial wastes which can be handled by distillation include:
Plating wastes containing an organic component -
usually the solvents Hre evaporated and the organic
vapors distilled.
Organic effluents from printed circuit boards are
i
adsorbed on activated carbon. Regeneration of the
activated carbon gives a liquid which is distillable
for recovery of the organic component.
Phenol recovery from aqueous solutions is a major
waste treatment problem. The recovery process
uses a polymeric adsorber. The adsorber is
7.8
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regenerated using a vaporized organic solvent.
A complex distillation system is used to recover
both the regeneration solvent and the phenol.
Methylene chloride which contains contaminants
is a disposal problem, but it can be salvaged
for industrial application by distilling.
Methylene chloride can be recovered from poly
urethane waste,
The separation of ethylbenzene from styrene and
recovery of both.
Waste solvents for reuse in cleaning industrial
equipment. Usually a mixture of acetone (ketones)
(alcohols) and some aromatics (Berkowitz, et al.
1978).
7.4 EVAPORATION
Evaporation is the vaporization of a liquid from a solution or a slurry
for separation of liquid from a dissolved or suspended solid or liquid. The
basic principle underlying evaporation is to concentrate a solution consisting
of a non-volatile solute and a volatile solvent (Arthur D. Little, Inc.,
1976). This is usually achieved by condensation of steam on metal tubes,
which have the material to be evaporated flowing inside them. The solvent,
which is in a vaporized form after the evaporation process, may be discharged
as an exhaust or can be condensed, purified, if necessary, and reused.
Similarly, the residue from the evaporation process, which is called the con-
centrate, can be disposed of or the useful materials in it may be reused. A
typical example where both the condensate and the concentrate can be recycled
7.9
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back to the original process where these materials are used Is the electro-
plating industry.
7.4.1 Process Configurations
Basically, there are two types of evaporation systems, namely atmo-
spheric evaporation and vacuum evaporation. Atmospheric evaporation can be
accomplished simply by boiling the liquid. Evaporation can be achieved at
lower temperatures by spraying the heated liquid on a surface and blowing air
over the same surface.
In vacuum evaporators, the boiling temperature is reduced by lowering
the evaporating pressure. The water vapor is condensed and the non-conden-
sible gases are removed by a vacuum pump. Vacuum evaporation aiay be either
single or multiple effect.
Single effect evaporators are used v;here the required capacity is
small, steam is cheap, the vapors on the liquids are so corrosive that very
expensive materials of construction are required, or when the vapor is so
contaminated that it cannot be reused (Arthur D. Little, Inc., 1976).
In a multiple-effect evaporator,, steam from sn outside source is condensed in
the heating element of the first effect. The vapor produced in the first
effect is used as the heating medium of the second effect, which is operating
at a lower pressure than the first effect. The vapor from the second effect
is used as the heating medium for the third, and so on. Each consecutive
effect operates at a lower pressure th'an the preceding effect.
Several types of evaporators are used for the separation and recovery of
different organic and inorganic compounds. In process lndustriess such as
metal and plastics finishing industries and particularly the electroplating
industry, closed-loop recycling of wastes is achieved by using evaporation as
7.10
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a recovery process. In a closed-loop system, the condensate and the concen-
trate are recycled back to the rinsing and plating operations respectively,
thereby forming a closed-loop treatment.
7.4.2 Evaporation: State of the Art
A survey done by Plating and Surface Finishing journal (Anonymous, 1979)
concluded that a favorable payback for evaporative equipment is achieved for
the recovery of chromium, nickel, and lead-tin alloy plating chemicals but
not for zinc cyanide solutions. It was felt that operating costs for recovery
equipment exceeded the saving in zinc plating chemicals. However, recovery
may be justified because it eliminates costly cyanide destruction, zinc
precipitation, and solids separation. There does not seem to be much informa-
tion available in this area and more research is needed to study the applica-
tion and cost analysis of evaporation systems for recovering zinc plating
chemicals.
Recovery of industrial pollutants by evaporative techniques becomes more
cost-effective when the pollutants in the wastes are in high concentrations
and the flow rates are low. In order to achieve this, inultistate counter-
i
current rinse tanks are suggested in the case of the electroplating industry.
As mentioned earlier, one of the major limitations of evaporation
techniques is the cost of heating from steam generators. This may be sub-
stantially reduced by utilizing waste heat from the plating baths of the
electrochemical industry (Cheremisnoff, e_t _al. 1977; Hall, ejt _a^. 1979;
Skornonek and Stinson, 1977). More research is warranted in this area to
determine the feasibility and economics of utilization of waste heat.
Another way to economize on energy consumption is to use multiple-effect
evaporation technique, in which the vapor produced from one effect is used as
7.11
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the heating medium for che next one. In fact, one electroplating company
abandoned its use of a single-effect evaporator for nickel recovery because
operational costs were greater than the value of the recovered nickel and
calcium ions and other impurities resulted in the cioggirg of anode bags.
This company now uses three counter-flow rinses to concentrate and recover
nickel salts from Its rinse water waste and periodically dumps the fourth
final riuse to control impurities (Anonymous, 1979).
In the case of cyanide copper plating operations, certain types of
evaporation techniques (for examplot climbing film evaporators), may not be
used since the materials of construction in use are appropriate only for acid
pH. Different types of materials are needed in such cases (Hall, et_ al.
1979).
7.4.3 Process Modifications
Ideally, evaporation results in a concentrate and a deionized condeusate.
But in a practical situation carry over of some impurities in the condensate
may occur. Furthermore, the concentrate may also contain organic brighteners
and an:i-foaming agents. An activated carbon bed may be necessary to remove
such impurities before the condensate is recycled back (Hall, et_ al_., 1979).
Similarly, impurities may be found in the concentrate, which can also be
purified by several types of treatments.
In order to recover copper from copper cyanide plat.'.ng operations, the
concentrate may be treated with peroxide, caustic potash, and activated
carbon (Hall, &t_ &L. 1979).
In the case of nickel plating operations, (Atimion, 1930) reported that
when the nickel solution is sufficiently concentrated from evaporation, it is
pumped from the evaporator to a stainless steel tank for carbon treatment at
7.12
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pH 1.5 to 1.7. The solution is then filtered into a clean tank and nickel
carbonate is added to the solution to raise the pH to 5.0 to 5.5. Then
required doses of potassium permanganate and activated carbon are added to
remo.ve sulfur. After settling for eight hours, the treated solution is
filtered twice and recycled to the plating bath.
Pretreatment of the wastewater is sometimes necessary to make the
evaporation process applicable to a given situation. For example, roost of
the companies using evaporators to recover chromium solution have installed
cation exchangers to control the concentration of trivalent chromium and
other metallic impurities that tend to reduce cathode efficiency on the
plating (current density) range (Anonymous, 1979; Hall, et_ al. 1979; Kolesar9
1972; Cheremisnoff, e_t al. 1977). In the case of cyanide plating, purifi-
cation is accomplished by precipitation of carbonate, which is best done at
the point of maximum concentration (Cherernisinoff, et al. 1977).
7.4.4 Limiting Technology
There do not seem to be any fundamental limitations on the applicabi-
lity of evaporation process, however, energy consumption appears to be the
major obstacle. There are certain practical limitations in the application
of evaporators. In addition to heat transfer characteristics and economic
energy utilization, the other variables that limit the practical application
of evaporation process are crystal formation, salting, scaling, corrosion
entrainment, and foaming (Arthur D. Little, Inc., 1976).
In order to prevent these problems in evaporators, studies should be
conducted to determine the proper type of evaporation for a given industrial
operation. Information in this area seems to be scarce.
It seems that most of the work on application of evaporation techniques
7.13
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used for the recovery of industrial pollutants has been done in the electro-
plating industry. Evaporation systems are also used by the paper industry to
recover the chemicals from the Kraft pulping process (Arthur D. Little, Inc.,
1976). More research needs to be done to determine the applicability of
evaporation techniques for recovery of inorganic compounds in other industries,
7.4.5 Recycle, Recovery, and Reuse Applications
Evaporation is a well-defined and well-established process that has been
used in several industrial operations for a number of years. There probably
is no chemical industry at this time which does not use evaporation systems
of one kind or another. The evaporation process is used for a variety of
purposes including dehydration, crystallization, separation, concentration,
and recovery of various industrial chemicals.
V.5 REFRIGERATION
The production of cooling, or heat withdrawal, may be accomplished by
the solution, melting or evaporation of a substance, or by the extension of
a gas. The term refrigeration refers particularly to cooling below atmo-
spheric temperature. Machines which produce cooling may be classified into
compression and adsorption refrigeration machines, depending on the mode of
recovery and circulation of material.
Compression refrigeration machines evaporate low-boiling liquids and
i
condense their vapors or gases. Mechanical energy is used to effect com-
pression of the refrigerant, following compression, where it becomes liquefied
through heat transfer. The refrigerant is then sent from the condenser to
the evaporator where it withdraws heat by evaporation and is recycled for
compression. Electric energy may also be used to compress the refrigerant
and turbo-compressors driven by electric motors or steam turbines may be used
7.14
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instead of piston compressors.
Adsorption refrigerating machines utilize hear, to produce cold, and
operate economically when waste heat is available. They are especially
useful for low temperature evaporation pressures. Refrigerant leaving the
evaporator travels to an adsorber where it is bound by the aid of a liquid
pump. After passing through a heat exchange, it travels to a stripping
tower, where the refrigerant is stripped from the water by the addition of
heat. The gas is then liquefied in the condenser. The mechanical compressor
used in compression refrigerating machines is substituted by a thermal com-
pressor in adsorption refrigerating machines (Perry, 1963).
In practice, vapors undergoing refrigeration are condensed by either
contacting a cold surface or by contact with the coolant. When a vapor is
refrigerated for the purpose of emission control of product recovery, the
unit in which heat transfer takes place between the refrigerant and the vapor
is referred to as the condensor. In a surface condenser, the coolant does
not contact the vapors or condensate. Coolant, vapors and condensate are
intimately mixed in contact condensers.
The choice of condensor will be influenced by a) the presence of moisture
with the vapor, b) the operating temperature level and c) whether or not the
condensed vapors are to be reused as product liquid. Cooling an air-vapor
stream condenses the moisture to liquid at temperature above 32 F. This may
lead to a gradual build up of frost which can be removed by scrapevs or by
periodically raising the surface temperature above 32 F. A contact conden-
sor does not lend itself to frost removal, since any solid which is formed
circulates with the contact and condensate, impairing the performance of
pumps and valves (Honegger, 1979).
7.15
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7.5.1 Limiting Technology
In the case of hydrocarbon recovery, removal efficiency by refrigeration
depends on the hydrocarbon concentration of inlet vapors.
The degree of produce recovery by refrigeration is also dependent on the
refrigeration temperature level. The more volatile the product, the lower
the temperature required for effective recovery. When moisture is entrailed
in the vapor, special equipment may be necessary to accommodate the ice and
frost which build up, impairing process performance.
7.5.2 Recycle, Recovery, and Reuse Applications
Refrigeration is ons of several competing methods for recovering emis-
sions from bulk liquid transfer and storage operations, ard has been promoted
for vapor recovery at gasoline loauing racks. Equipment and operating costs
are relatively high for this application because ultra-low temperatures are
required for effective recovery (Honeggert 1979).
At some gasoline terminals, vapors are compressed and then refrigerated
to obtain condensation. Other installations omit compression and refrigerate
the vapors to temperature approaching 73 C (100 F). Removal efficiencies
depend on the hydrocarbon concentration of inlet vapors. In the case of
saturated hydrocarbons, removals of greater than 96 percent are possible.
Similar systems have been proposed for marine petroleum terminals (Anonymous,
1978).
The degree of product recovery is also dependent on the refrigeration
temperature level. The more volatile the product, the lower the temperature
required for effective recovery. Since many hydrocarbon vapors require
temperatures below the point at which water freezes, special equipment may be
necessary to accommodate the ice and frost which form due to moisture
7.16
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entrained in the air (Honegger, 1979).
7.17
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BIBLIOGRAPHY
Anonymous (1974) Condensation of Stream Turbine Exhausts
British Pat. 1,361,025. " ~
Anonymous, (1978) Control Techniques for Vj>2jitjle_Orj;.Tnic
Enissions from Station.iry Sources. U.S. EPA, Office
of Air and Waste ManugL-ment, !il>A~4 jQ/2-78-022.
Anonymous, (1979) "Recovery Pays." Plating and Surface Finishinr,
66, 2, 45-48.
Anonymous, (1980) "Solvent Recovery System Saves Costs and
Clean Air". J. Chem CHR. 87(5):91,S2.
Arthur D. Little, Inc., (1976) "Physical, Chemical and Biological
Treatment Techniques In Industrial Wastes, Vol. II." National
Technical Information Service: PB-275, 287.
Atimion, L., (1980) "A Program of Conservation, Pollution Abatement."
Plating and Surface Finishing. 67, 3, 18-20.
Berkouitz, J.B., et al., (Nov., 197o) Physical, Chemical, and Biological
Treatment Technique for Industrial Wastes. NT1S //PB-275 054.
Cheremisinoff, P.M., A.J. Perna, and J. Ciancta, (1977) "Treating Metal
Finishing Wastes, Part 2." Industrial Wastes, 23, 1, 32-34,
Hall, E.P., DoJ, Lizclas and E.E. Auerbach, (1979) "Recovery Techniques in
Electroplating." noting and Surface Finishing. 66, 2, 49-53.
Honegger, R.J., (1979). "Refrigeration Methods of Vapor Recovery,"
Technol. Kept. Card Inc., A subsidiary of GATX.
Jones, J.F. (1974) "Clean Fuels front Coal for Power Generation".
Preprint, Arner. Chem. Soc. (Presented at the Atner. Chem. Soc.
Storch Award Syrap., Atlantic City, K.J., Sept. 11).
Kolesar, T.J., (1972) "Closed-Loop Recycling of Plating Wastes."
Industrial FiniBtiing, 48, 9, 22-25.
Perry's Chemical Eng. Handbook. (1963) McGraw Hill.
Pruessner, R.F. and L.O. Broz (1977) "Hydrocarbon Emission Reduction
Systems". J. Chera. Eng. Prog. 73(8):69-73.
Skovronek, H.A., and M.K. Stinson, (1977) "Advanced Treatment Approaches
for Metal Finishing Wastewaters: Part 1." Hating and Surface
Finishing, 64, 10, 30-38.
7.18
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Steinberg, M., and Seller, M. (1964) Brookhaven National Laboratory
Report.
Theodore, L., and A. Buonicore (1975) "Vapor Control by Condensation
Performance Equations and Design Procedures" Proc, APCA 68th
Vol. 2 paper 75-23.2.
Williams, K.R. and N. Van Lookeren Campagne (1971) "Synthetic Fuels
from Atmospheric Carbon Dioxide". Preprint, Shell Intl. Petrol
Co., Ltd., London and Shell Intl. Petrol Maatshappig N.V., The
Hague (Netherlands).
7.19
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CHAPTER 8
SECTION II
CHEMICAL MODIFICATIONS
8.1 INTRODUCTION
Chapter 8 of this report examines several chemical trenCmenc processes
currently being used to recover heavy metals from industrial sludges and
wastewaters. The processes to be discussed include:
1. Cementation
2. Precipitation
3. Catalytic Hydrogenation
4. Reduction
For each of the above listed processes, the following areas will be discussed:
1. Process Description
2. Recycle, Recovery, Reuse and Applications
3. Statement of Limiting Technology.
^
The "Recycle, Recovery and Reuse Applications" section will discuss the past
and current work using each process in the recovery of heavy metals from
industrial wastewaters. The "Limiting Technology" section discusses the
i
advantages, disadvantages and limitations of each process in its application
of removing as well as recovering the metals.
8.2 CEMENTATION
Cementation is the recovery of an ionized metal in solution by spon-
taneous electrochemical reaction to its elemental state through the oxidation
of another eleaental metal which is also kept in solution. The process can
be predicted in terms of electrode potentials. The metal with more positive
oxidation potential in the electromotive series will pass into solution
8.0
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displacing a metal with a less positive potential. Since, In electrodeposi-
tion, the less noble metal goes into solution, scrap iron is often chosen as
the reductant because of its low cost.
The cementation process is conutionly used to recover copper tailings.
Streams bearing copper ions are passed through a series of re-action tanks
containing scrap iron, where the copper is removed as elemental metal and the
iron is displaced into solution. The reaction is as follows:
The cementation process generates electrodeposits without external
current. For exatple, an electropotential sufficiently large to deposit
copper is produced when copper ions and iron surface are present in the
aqueous solution.
The process can be described as a galvanic corrosion cell. A cathodic
copper deposit covers the anode except for sub-microscopic regions from which
Iron is being the basic matal, in the mariner of a short-circuited galvanic
cell. These anodic sites effectively migrate around the surface of the iron;
therefore the entire piece of iron can be consumed. The copper deposits can
be stripped from the surface of the iron through vigorous stirring or agita-
tion and the resulting copper sludge can be carried as high purity cop, »r
(Patterson and Jancuk, 1977). Iron is less toxic than copper and can be
readily oxidized by air and removed from solution.
If hexavalent chromium is also present along with copper in the waste-
water, during the process of cementation, the former may react with either
elemented on ferrous iron to yield trivalent chromium (Jester and Taylor,
1973).
2 Cr+6 -f 3le° * 2Cr+3 + 3Fe+2 (8.2)
8.1
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Cr +6 + 3Fe+2 *• Cr+3 + 3Fe+3 (8.3)
8.2.1 Limiting Technology
The cementation process has been proven to be effective for the removal
ana recovery of copper from waete streams of small flow. It has not been
exploited for larger flows duo probably to the need for longer contact time
with che metallic interface.
There seems to be an excess iron consumption (i.e., more than needed
on the basis of stoichiometry) associated with the process due to some side
reactions of iron in the wastcwater. Disadvantages of excess iron consumption
include wastage of the metallic iron reactant and production of unnecessary
amounts of iron sludge upon precipitation treatment.
Thertnodynamic limitations and the need for process optimization seem to
prevent the removal of copper to the low levels required in most effluents.
Therefore the residual copper levels after cementation treatment would normal-
s'
ly require additional costs to the overall treatcier.t.
The cementation process for recovery of metals seems to be in an infant
stage and needs to be studied more.
8.2.2 Recycle, Recovery, and Reuse Applications
The cementation process is employed to a very limited extent by industry
today. The hydrometallurgical indu'stry employs the cementation process for
the recovery of such metals as copper on iron, silver and gold on zinc, lead
on iron or zinc, palladium on copper, thallium on zinc, gold from gold
chloride on cadmium, and gallium on aluminum (Habashi, 1970).
A few industries have set up wastewater treatment operations for chromium
reduction and copper recovery uainfi the cementation process. The Anaconda
American Brass Company utilized the cementation process as outlined by their
8.2
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patent for copper recovery. The copper sludge from their treatment plant
contained 30-40% moisture with 70-80% elemental copper on a dry bajis.
The Scovill Manufacturing Company in Waterbuiy, Connecticut adapted the
Anaconda approach and designed a process for a simultaneous chroming reduction
and copper removal (Jester and Taylor, 1973). The copper sludge from this
operation contained more than 90% elemental copper by clrv weight.
Other known applications of cementation include copper recovery from
warar pickle liquor in a brass mill (Dean, £t aJL., 1972), and the reduction
of cobalt and vanadium with iron metal in the treatment of waste ammonium.
persulfate etching solutions (E. M. Songio, cited in Jancuk, 1976).
Industrial application of cementation process for copper recovery
produced a mud of about 30-40% moisture, with the dry weight analysis of 95-
99% (Keyts, 1966), 70-80% (Jester and Taylor, 1973; Case, 1975) pure copper.
8.3 PRECIPITATION
Chemical precipitation is the most common method for removal of inorganic
heavy metals found in industrial waste effluents. Precipitation of a heavy
metal ion occurs when the salt with which it is in equilibrium reaches its
solubility limit, as defined by its solub5lity product. The value of the
logarithm of the solubility products of different metal saltG are available
in the literature (Bard, 1966; Feitknecht and Schindler, 1963; Kartell and
Smith, 1974a, 1974b, 1974c, Sillen end Kartell, 1964, 1974). These constants
raay be used to plot the theoretical solubility diagrams for each metal which
can be used for determining the pH levels at which each metal is least
soluble. An example of such diagrams is s'.iown in Figure 1.1 for various
metals as hydroxides in pure water.
Theoretical solubility diagrams such as tho^e shown in Figure 1.1 can be
8.3
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used only as approximations for determining the pH levels at which each metal
can be precipitated in the greatest quantity as a given salt, since the
solubility of metals may vary in aqueous solutions depending upon temperature,
ionic strength, and the presence of anions or other completing agents in
solution (Butler, 1964; Stumm and Morgan, 1970).
Most of the inorganic heavy metals generally found in industrial waste
effluents are removed by precipitation as hydroxides. The process of precipi-
tation involves the adjustment of pH of the waste stream by addition of an
acid or an alkali, and coagulating to effectively remove the resultant
hydroxide through classification and/or filtration. Metals may also be
removed by precipitation as sulfides. Metal sulfides are generally more
insoluble in water systems than, corresponding hydroxides. However, one
of the limitations of L.alfide precipitation is that sulfides can hydrolyze
to form extremely noxious hydrogen sulfide gas.
Chemical precipitation of heavy metals may be accomplished by other
batch or continuous treatment systems. Equalization of the waste stream may
be necessary for continuous systems if the flow and pH of the waste vary
widely with time. The first process step is the adjustment of the pH by
addition of acid or alkali to achieve the defined pH level for optimum preci-
pitation. A polymer is usually added to aid coagulation. The waste stream
then flows into a sedimentation tank, where the heavy metal precipitate
settles out. Precipitated sludge may be recirculated to the precipitation
tank in order to provide a seed which will aid agglomeration of the newly
formed precipitate.
The chemicals most frequently used for precipitation of raetals are lime,
caustic soda and sodium carbonate. Lime is preferred because of its relatively
8.4
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lower cost, caustic is used in small installations where daily chemical costs
are not significant, and soda ash is used in cases where it provides a batch
chemical reaction (e.g. cadmium and nickel precipitation) (Lanouette, 1977).
8.3.1 Limiting Technology
Although the solubility of many metallic compounds is extremely low in
pure water, such levels can not be achieved in industrial effluents alter
precipitation processes, because of the presence of complexing agents, which
tie the metals in solution. Furthermore, when two or more metals are found
in the sarae waste stream9 the problem becomes even more complex, since the
optimum pH for precipitation may be different for each ion. The question
then becomes whether to treat the waste at a pH vhich would produce satis-
factory, but not optimum results for each of the metal ions present in the
wastewater,, or to treat It at the optimum pH for one metal ion, remove that
metal precipitate, and then treat for the second metal ion and so forth.
8.3.2 Recycle, Recovery, and Reuse Applications
The precipitation process is used in full-scale treatment of many
industrial wastewaters containing,heavy metals. Wastewater streams from the
iron and steel industry (USEPA, 1974), metal finishing industry, (FWDA, 1968)
and inorganic chemical industry (USEPA, 1975) are some typical examples which
L
receive precipitation treatment f
-------
be sent to a reprccessor for recovery of cadmium.
Chromium is found in either hexavalent or trivalent form. Hexavalent
chromium is found in the waste streams' of plating operations, aluminum
anodizing, and paint and dye operations, while trivalent chromium is common
in effluents from .the photographic, ceramic, and glass industries (Lanouette,
1977). Treatment for chromium usually consists cf reduction of hexavalent
chromium to its trivalent form and precipitation of the trivalent chromium
by addition of lime or caustic to increase the pH to between 7.5 and 8.5,
where minimum solubility of chromium hydroxide occurs.
Lead which is found in waste effluents from battery manufacture, and
printing, painting and dyeing operations can be precipitated with lime or
caustic soda to form lead hydroxide; with soda ash to form lead carbonate; or
with trisodium phosphate to form lead phosphate.
The standard method of removing mercury is to adjust the pH to 5 to 6
with K-SO, and then add sodium sulfide to an excess of 1-3 tng/1. This forms
an insoluble mercury sulfide, from which the metal can be recovered,
8.4 CATALYTIC HYDROGENATION
Catalytic hydrogenation is a useful method for achieving controlled
transformation or organic compounds. The reaction is carried out easily and
produces high yield of a product free of contaminating reagents. Satisfactory
results can often be obtained over a wide range of conditions of temperature,
pressure, and degree of agitation, factors which can affect both activity and
selectivity in catalytic hydrogenation.
In any liquid phase hydrogenation, hydrogen moves from the gas phase
across a gas-liquid interface and from the liquid phase across a liquid-solid
interface to the external surface of the catalyst and then into its porous
8.6
-------
structure. The net movement of hydrogen to the catalyst results from con-
centration gradients which develop when hydrogen is consumed by the catalytic
reaction. In many cases the reaction rate is limited wholly or partially by
the speed with which hydrogen is transported to the catalyst surface. Mass
transport is more likely to become a limiting factor as a catalytic activity
increases.
Due to mass transport limitations on the rate of hydrogenation, hydrogen
availability at the catalyst surface may vary from a condition in which the
rate of reaction is controlled almost entirely by the rate of chemical reac-
tion to one in which the rate is controlled completely by the rate of hydro-
gen transport to the active catalyst site.
The process of hydrogenation takes place in a reaction which brings
hydrogen, the catalyst, and the substrate into contact in the absence of air.
Most hydrogenations are carried out in batch-type reactors, although in some
cases, especially large-scale processes, continuous reactors are used..
Reactors may be built for hydrogenation at atmospheric pressure, low pressure,
and high pressure. Fixed-bed reactors are useful in the hydrogenation of
large volumes of material, and nay take the form of a trickle bed, in which
a liquid phase and hydrogen flow concurrently downward over a fixed bed of
catalyst particles, or a flooded bed, in which hydrogen and the liquid pass
concurrently upward.
Hydrogenation catalysts differ widely in activity and selectivity, with
these characteristics determined mainly by the major metal component.
Metals can be ordered into a hierarchy of activity for hydrogenation of each
functional group. Noble metal batch-type catalysts usually contain between 1
and 10% metal; fixed-bed catalysts usually contain 0.11.0%. On a weight of
8.7
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metal basis, activity is linear with metal ccacontration over a limited
range. As metal concentration increases, metal becomes piled upon metal,
making an increasing percentage unavailable for use. On a weight of raetal
basis, the more dilute the metal, the more efficient the catalyst, but the
amount of catalyst (metal plus support) needed to maintain a constant weight
of metal increases directly as the metal concentration decreases. A compro-
mise is made between making the most efficient use of metal and the economic
need to minimize the amount of catalyst used. Supported base metal catalysts
usually contain much more metal than noble metal catalysts.
Two catalysts used in combination may sometimes give better results than
either used separately. Synergism has been explained by the assumption that
hydrogenation involves multiple intermediates, some of which may be reduced
more easily by one catalyst and some by the other. The second catalyst may
also function by its superior ability to remove catalyst inhibitors formed in
the reaction.
Catalyst poisons vary from reaction to reaction. Poisons included heavy
metal cations, halides, divalent sulfur compounds, carbon monoxide, aminess
i
phosphines, and in some cases, the substrate itself or sorae product of the
reaction. Small amounts of a certain substance my be beneficial to catalyst
functioning, while larger amounts will be poisonous. A quantitative measure
of catalyst poisons can be made byj carrying out the same hydrogenation at
different catalyst loadings. If the rate increases more rapidly than the
increase in amount of catalyst, the presence of a poison is confirmed.
Small quantities of various substances which favorably affect catalyst
life, activity, or selectivity may be termed prompters. The effect a promoter
may have also depends on the reaction which the catalyst is used. There is
8.8
-------
little theory on which to base the use of promoters, and their successful use
usually proceeds from an extension, or modification of something already
known.
Heterogeneous hydrogenation catalysts may be either supported or unsup-
ported, the former type being further divided into those for use in slurry
processes and those for use in fixed bed operations. Catalysts used in
slurry processes are usually fine powders, while fixed-bed catalysts are
usually in the form of cylinders, spheres, or granules. A good carbon or
alumina will be suitable as a catalyst support for the majority of reactions.
Solvents may be used to increase ease of handling and catalyst recovery,
to moderate exothermic reactions, increase rate and selectivity, and permit
hydrogenation of solid material. Most liquids which are stable under hydro-
genation conditions and which do not inactivate the catalyst can be used as
solvents. Commonly used solvents include acetic acid, methanol, and ethanol.
A problem which may arise during the hydrogenation process is the
agglomeration of the catalyst. This will have an adverse effect on the rate
and may even cause the reduction to fail. Agglomeration can often be over-
come by changing the pH of the medium or by changing the solvent, the solvent-
substrate ratio, or the catalyst support.
Lost catalytic activity may in some cases be restored by regeneration.
Regeneration techniques are basically a variation or combination of oxida-
tions, hydrogenation, steaming, heating, or solvent wash. It is difficult
to predict in advance which procedures will work. Eventually, a catalyst can
no longer be sufficiently regenerated. Noble metal catalysts can then be
returned to a refiner and destroyed, if volume warrants, for subsequent
recovery of the pure metal. Base metals may or may not be reclaimed (Rylander,
1972).
8.9
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8.A.I Limiting Technology
Catalytic hydrogenation is a useful method for achieving controlled
transformation of organic compounds.
Due to mass transport limitations on the rate of hydrogenation, it may
vary from a condition in which it is almost entirely controlled by the rate
of chemical reaction to one in which it is controlled completely by the rate
of hydrogen transport to the active catalyst site.
Hydrogenation catalysts differ widely in activity and selectivity, with
these characteristics determined mainly by the major metal component. Both
activity and selectivity are influenced by conditions of temperature, pres-
sure, and degree of agitation.
Solvents may be used to increase ease of handling and catalyst recovery,
moderate exothermic reactions, increase rate and selectivity, and permit
hydrogenation of solid material.
Agglomeration of the catalyst is a problem detrimental to the hydrogena-
tion process which may be overcome by changing the pH of the medium, changing
the solvent, the solvent-substrate ratio, or the catalyst support. Catalytic
poisoning is another problem which can affect hydrogenation.
It is difficult to predict a regeneration technique suitable for specific
catalyst. Eventually, a cr.talyst reaches a point after which it can no
longer be sufficiently regenerated.
Small quantities of substances which favorably affect catalyst life,
activity, or selectivity may be termed promoters. Although the effect of a
promoter depends on the reaction in which the catalyst is used, there is
little existing theory on which to base successful choice of a promoter.
8.10
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8.A. 2 Recycle, Recovery, and Reuse Applications: Inorganics
Wilson (1971) describes a process in which hydrogen is recovered from
gases in which it is concentrated at greater than 20% by volume. In this
process, a hydrogen-extracting aromatic hydrocarbon is introduced counter-
currently to the system. Following hydrogenation, the aromatic hydrocarbon
is sent by countercurrent flow to a dehydration catalyst zone. The process
results in the recovery of a hydrogen-containing gas of 90 volume %.
Sulfur recovery may be effected through implementation of a process
described by Rowland (1970). Sulfur present in tail gas is converted to pure
hydrogen sulfide by hydrogenation under moderate conditions of temperature
and pressure. A cobalt molybdate catalyst is effective in reacting water
vapor with CO to COS and CS2 to form H»S. Following hydrogenation and cooling,
H_S is removed and converted to sulfur by the Stretford process, or by recycle
to the reaction furnace of a sulfur plant.
8.4.3 Recycle, Recovery, and Reuse Applications: Organics
\l
Substitute natural gas may be produced from whole crude oil fractions
boiling above naphtha. Components of the process include a reaction system,
a quench system, gas purification and secondary hydrogenation areas, and a
i
gas drier. Preheated oil and hydrogen gas are reacted in a fluidized bed of
coke particles, resulting in the production of a rich gas with & concentration
i
of methane and ethane. The gas is quenched with a circulating stream of
light aromatic to effect separation of liquid products. Hydrogen sulfide is
removed from the rich gas in an absorption-stripping system and converted to
elemental sulfur in a Claus plant.
In the secondary hydrogenation section, purified gas is contacted with
a catalyst in a fixed bed reactor. Ethane contained in the gas reacts with
hydrogen to produce methane. In cases in which there is an excess of hydrogen
8.11
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to ethane, carbon dioxide or hydrocarbons such as liquified petroleum gas are
added upstream of the secondary hydrogenation step, resulting in product gas
containing less than 5 mole "L hydrogen (McMahon, 1972) .
Diolcfins and olefins may be selectively removed from the product
gasoline obtained in light olefin manufacture resulting in the recovery of
usable hydrocarbons. Parker (1%7) describes a process in which an aromatic
hydrocarbon feedstock containing diolefins, tnono-olefins, and sulfur contami-
nants is hydrogenated at a temperature of 200-500 F with a composite catalyst
of lithium in palladium-alumina to convert the diolefins to raono-olefins.
The effluent is separated and an aromatic hydrocarbon is then hydrogenated at
a temperature of 550-750 F with a conventional desulfurization catalyst to
saturate olefins and convert sulfur compounds to hydrogen sulfide. Hydro-
carbons suitable for gasoline blending and aromatic hydrocarbons suitable for
solvent extraction are recovered as separate product streams,
8.5 CHEMICAL REDUCTION
Chemical reduction is a widely used industrial waste treatment process,
which has the potential for recovering pollutants such as metals. This
process is primarily applied to the control of hexsvalent chromium in the
plating and tanning industries.
Reduction and oxidation reactions take place conccramitantly and so the
overall process is referred to as an oxidation-reduction (redox) reaction. In
a redox reaction, the oxidation state of at least one resctant is raised
while that of another is lowered. In the following reaction:
-f 3502 J Cr2(S04>3 + 2H20 (8.4)
hexavalent chromium (oxidation state 6+) is reduced to trivelent chromium
(oxidation state 3+) , while sulfur is oxidized with an increase in its
8.12
-------
oxidation state from 2+ to 3-K Sulfur compounds and base metal components
such as those of iron, zinc and sodium are the more common reducing agents.
8.5.1 Limiting Technology
Most of the applieat.ious of chemical reduction technology to industrial
waste treatment to date have been for dilute waote streams. Chemical reduc-
tion has limited applicability to slurries on sludges in their original form
because of the difficulties of achieving intimate contact between the reducing
agent and the pollutant to be removed. One of the disadvantages of chemical
reduction is that it introduces new metal ions into the effluent stream. If
the level of these new contaminants is high enough to exceed effluent guide-
lines, additional treatment will be required, adding more cost to the overall
treatment.
8.5.2 Recycle, Recovery, and Reuse Applications
The two most common applications of chemical reduction processes are the
removal of hexa chromium from plating and tanning industries and the removal
of mercury from caustic/chlorine electrolysis cell effluents.
In plating and tanning industries, sulfur dioxide is mostly used for
reducing hexavalent chromium to trivalent chromium, which is then precipitated
as Cr(OH), with either lime or sodium carbonate. The waste is then subjected
to sedimentation, which separates the solids portion.
The reaction equations are as follows:
S02 + H20 J H2S03 (8.5)
+ 3H2S03 £ Cr2
-------
sodium borohydridc (NaBH) la mixed with the vastewatcr, which results in the
reduction of ionic mercury to metallic mercury. The latter precipitates out
of solutions, which can be recovered for recycle.
Sodium borohydride is also used for reducing lead and silver compounds
from industrial effluents- These compounds are usually reduced chemical
metals, which can be precipitated, settled and recovered for reuse.
8.14
-------
BliiLlO'JRAPHY
Anonymous. (1973). "Copper Indus fry Uees Much Prerap Iron." Environ. Scl.
Tcchnol. 7(2):100-102.
Bard, A.J. (1966). ChcIDicg 1 Egui_lxbr{nin. Harper and Row, New York, N.Y.
Butler, J.K. (1964). Ionic Equilibrium: A Matbj.-n^tJ£al_A2£ro£ch. Addison-
Wesley Publishing Company, Inc., Reading, Mass.
Case, O.P. (1974). "Metallic Recovery from Wastewater Utilising Cementation."
EPA-670/2-74-009.
Case, O.P. (1975). "Copper Recovery from Brass Mill Discharge by Cementation
with Scan Iron." EPA 670/2-75-029 0PB-241822/6UP.
Dean, J.G., F.L. Basqui, K.H. Lanouette. (1972). "Removing Henry Metals from
Waste Water." Environ. Set. Tcchnol. 6(6);S18-22.
Federal Watef Quality Administration. (196S). "A State-Of-The-Art. Review
of Hetal Finishing Waste Treatment." Wat. Poll. Control Ret?. Ser. 12010
EIE 11/68.
Feitknecht, W. and P. Schindler. (1963).
Habarbi, F. (1970). Principles of Extractive Metallurgy. Vol. 2. Hydro-
metallurgy, Gordon and Breach, New York, NY.
Jancuk, W.A.D. (1976). "The Cementation Process for Heavy Metal Renoval fr&ra
Wastewater." Master of Science Dis-sereation, Illinois Institute of
Technology, Chicago.. IL p. 92.
Jester, T.L., and T.H. Taylor. (1973). "Industrial Waste Trcatreent at Scovill
Manufacturing Company." Proc. 28th Purdue Industrial Waste Confer.
129-137.
Keyes, H.E. (1966). "Copper Recovery Process," U.S. Patent 03,288,599.
Lanouette, K.H. (1977). "Heavymetals Removal." Chein. Eng. Desk Book Issue.
( ):73-30.
Kartell, A.E, and R.M. Smith. (1974a). "Critical Stability Constants. Vol 2:
Amines. ' Plenum Press, Hew York, SJ.Y.
Martell, A.E. and R.M. Smith. (1974b). "Critical Stability Constants. Vol.3:
Other organic Ligands."
Martell, A.E. and R.M. Smith. (197Ac). ^Cr it ical S tabi 11 ty_.Con st ant a, Vol. I, •
jnorganic Complexes.."
McMahon, J.F. (1972). "Fluidlzed Bed Hydrogenation Process for SNG."
i.. 68 (12>: 51-54.
8.15
-------
Parker, R.J. (1967). "Two-Stage Hydrogenation of an Aromatic Hydrocarbon
Feedstock Containing Diolefins, Monolefins, and Sulfur Compounds.' U.S.
Patent //3,494,35C .
Patterson, J.W. and W.A. Jancuk. (1977). "Cementation Treatment of Copper in
Wastewater." Proc. 32nd Purdue Industrial Waste Conference 853-865.
Rowland, L. (1970). "Ninety-nine Point Nine Percent Sulfur Recovery Unveiled."
Oilweek. 21(32):9-12.
NG/SNG Handbook of Hydrocarbon Process. 59(4):93-112.
Rylander, P.N. (1979). Catalytic Hydrogenation in Organic Synthesis. Academic
Press, New York.
Sillen, L.G. and A.E. Martell. (1964). Stability Constants of Metal-Ion
Complexes. Special Publication No. 17. The Chemical Society, London.
Sillen, L.G. and A.E. Martell. (1974). "Stability Constants of Metal-Ion
Complexes." Supplement No. 1. Special Publication No. 23. The Chemical
Society, London.
Stumm, W. and J.J. Morgan. (1970). Aquatic Chemistry: An Introduction
Emphasizing Chemical Equilibria in Matural Haters." Wiley-Interacience,
New York, N.Y.
U.S. Environmental Protection Agency. (1974). "Development Document for
Effluent Limitations.! Guidelines and New Source Performance Stsndardss-
Iron and Steel Industry."
Wilson, R.F. et al. (1971). Hyjjrogen Recovery Process. U.S. Patent
03,575,690.
SUPPLEMENTAL REFERENCES
American Enka Co. (1971). "Zinc Precipitation and .Recovery from Viscose
Rayon Wastewater." U.S. Environmental Protection Agency, Hater Pollution
Control Research Series No. 12090 ESG.
Arthur D. Little, Inc. (1976). "Physical, Chemical and Biological Treatment
Techniques for Industrial Wastes." OTIS Publication PB-275 287. pp.
23:1-23:33.
Cabe, V.P., B.L. Jones and R.D. Spellman. (1973). "Method for Simultaneous
Reduction of Hoxanalent Chromium and Cementation of Copper." U.S. Patent
03,748,124.
Dean, J.G., F.L. Bosqui and K.H. Lanouette, (1972). "Removing Heavyisetals
'from Wastewater." Environ. Sci. Tech. 6(6):51G-S22.
Faigenbaum, H.N. (1977). "Removing Heavymetals in Textile Waste." Ind. Waste.
8.16
-------
Huang, W. (1979). "Optimize Acetylene Removal." J Hydrocarb. Proc. 59(10):
131-132.
Jackson, D.V. (1972). MeCal Recovery from Effluents and Sludges." Metal
Finish J. 18(2)1); 23e, 237-8, 241-2-
Jacob!, J.S. (1966). Unit Processes in Ilydromcitallur^JLc.t'.JL Process. Van
Nostrand Inc. Princeton, N.J.
Lanouette, K.H. and E.G. Paulson. (1976). "Treatment of Heavymetals in
Wastewater." Poll. Eng.
Larsen, H.P., J.K.P. Shou and L.W. Roes. (1973). "Chemical Treatment of
Metal-Bearing Mine Drainage." J. Wat. Poll. Control Ass. ( ):1682.
Linstedt, C.P. et _al., (1971). "Trace Element Removals in Advanced Wastewater
Treatment Processes." J. Wat. Poll. Control Fed. 43(7?;15C7-1S13.
Metzner, A.V. (1977). "Removing Soluble Katels frora Wastewater." Water
Sewage Works. 124(4):98-loI.
Monninger, P.M. (1963). "Precipitation of Copper of Iron." Min. Congr. _J_.
49(1G):48-31.
Nadkarna, R.W., C.E. Jelden, K.C. Bowleg, H.E. Flandero end H.E. Wadsvorth.
(1967). "A Kinetic Study of Copper Precipitation on Iron." .Trans. Hits.
Soc. AIME. 239:581-565.
Peterson, R.J. (1977). H yd go j^e rta t ion Cat a ly s1 &. Koyes Data Cornorstion,
Park Ridge, New Jersey.
Rickard, R.S. and M.C. Fuerr;tenau. (1968), "An El'.>c£rocheaical Investigation
of Copper Cementation by Iron." Trans. Met Sc:^_AT.ME. 242:1487.
Scott, D.S. and II. Harlings. (1975). "Removal c,£ Phosphates and Metals from
Sewage Sludges." Environ. Sci. Tech. 9( }:846-855.
Steinberg, M. (1977). "S>-nthetic Carbonaceous Feul and Feedstocks frcrs
Oxides of Carbon and Nuclear Power." Energy (Res. and Dev. Adm.) Rept.
No.: CONF-770804-4 BN5-22785.
U.S. Environmental Protection Agency. (1975). "Development Document for
Effluent Limitations Guidelines and New Source Performance Standards
for the Prircary Copper Smelting Subcategory of the Copper Segment of
the Non-ferrous Metals.
8.17
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CHAPTER 9
SECTION II
PHYSICAL DISPERSION AND SEPARATION
9.1 INTRODUCTION
The sixth arid final chapter of this report will examine the "Recycle,
Reuse and Recovery Applications" of various physical dispersion and separation
processes. The processes included in this chapter are:
1. Filtration of Liquids
2. Filtration of Gases
3. Flotation
4. Liquid-Liquid Extraction
In addition to the Recycle, Reuse and Recovery Application section for each
process, a brief process description will be included and, in many cases, a
limiting technology statement will also be given,
9.2 FILTRATION OF LIQUIDS
Filtration is a physical process, in which solids suspended in ri liquid
are separated frora that liquid by psesage through a previous medium, which
separates and retains either on its surface or within itself, the solids
present in the suspension. In all filtration processes, a pressure differ-
ential is induced across upon the required aagnitude of the pressure differ-
ential, one or more of four types of driving force iaay be employed: gravity,
vacuum, pressure, or centrifugal. During the filter operation, a gradual
pressure drop occurs due to clogging or breakthrough of suspended matter.
When the pressure drop reaches a predetermined after prettet ^ent by air
scrubbing or a hydraulic surface uaah.
The filter media presently available in the commercial market can be
9.1
-------
divided into three general classes (Arthur D. Little, Inc., 1976):
1) A thick barrier composed of a layer of grenular media such as sand,
coke, coal, or porous ceraraics,
2) A thin barrier exemplified by a filter cloth on filter screen,
3) A thick barrier composed of a disposable material such as powdered
diatomaceous earth or waste ash.
The mechanics by which tlis; particles are removed in the filters are coaplex.
In surface filters, tiie predominant mechanism is usually simple mechanical
straining. However, in deep-bed filters, the mechanisms can include mechani-
cal straining coupled with gravitational settlings diffusion, interception,
inertial Ampaction, electrostatic interactions, chemical bridging, and speci-
fic adsorption phenomena within the filter mediua (Weber» 1972).
Basically, there are two types of filtration processes. Surface filters
perform cake filtration, in which the solids are deposited in the fora of a
l»
cake on the upstream side of a relatively thin filter medium. Deep filters
are used for deep-bed filtratior in which solids deposit within the uediwa.
Formation of a cake on the surface of a deep bed Is undesirable (Svsrovsky,
1979). Surface filters are noraally used for suspensions with siore than one
percent solids whereas dilute suspensions are treated by deep-bed filters *
The filter units, generally consist of a containing vessel, the filter
media, structures to support or retain the taedia, distribution and collection
devices for influent, effluent, and wastewater flows, supplements! cleaning
devices, and necessary controls for flows, water levels, or pressures. Seme
of the more significant alternatives in filter layout are discussed in an EPA
process design manual for suspended solids removal. (U.S. EPA, Jan. 1975).
A wide variety of filtration devices are consaercially available. How-
ever, they can be classified under the following categories having similar
9.2
-------
characteristics:
1. Deep Bed Filters:
Deep bed filters were originally developed for potable wator treatment
but presently they are increasingly used for industrial end municipal
wastewater treatment. The filter bed is usually contained within a
basin or tank and is supplied by an underdrain system vhich allows the
filtered liquid to be drawn off while retaining the filter medium in
place. The most cotnsson configuration of a deep-bed filter is the
downflou gravity design. The solids concentration i^ the feed should be
less than about 0.1% by volume in order to keep down the number end
volume of the vajher. The most common example of deep-bed filters is
the granular media filtern, which use a bed of granular particles
(usually sand from 0.4 to 2.5 trna in cise), as tha filter raedium. The
use of dual or multi-media filters is becoming increasingly cossmon. Such
filters have coarse material of low density for she top layer and
progressively finsr materials of increasing density for the lower layers.
An example of ti5nle media i_ a cositduation of anthracite, filter-sand,
and garnet.,
Deep-bed filtration is most often operated as a batch process. However,
continuous filters which continuously backwash a portion of the reedium
are not uneoERon. Some examples of such filters are hydroaatioa in-
depth filters, radial-flow filters, end traveling backwash filters.
(U.S. EPA, Jan. 1975).
2) Pressure Filters:
Pressure filters can treat feeds with concentrations up to ten percent
solids. Pressure filters may be grouped into two categories, plffite end
frame filters presses and pressure vessels containing filter element
9.3
-------
(Svarovsky, 1979).
The conventional plate and frame press consist of a scries of plat&s
and frames, alternately arranged in a stack and pressed together with
hydraulic or sciew-drewn rans. The plates are covered with a filter
cloth. The slurry is pumped into the frames and the filtrate is drained
from the plates. Filter media for plate and frame presses Include
various cloths, mats, and even paper. The second category of pressure
filters includes a number of available designs that feature a pressure
vessel containing filter elements. Some examples in this category of
filters are: rotary-drum pressure filters, cylindrical element filters,
vertical-tank vertical-leaf filters, horizontal tank vertical-leaf
filters, and horizontal-leaf filters (Svarovsky, 1979}» A few of the
above-mentioned filters are used for dewatering purposes and are die-
cussed in a separate report.
In addition to the filters discussed above, there are centrifugal
filters, fixed-bed centrifugal, moving-bed centrifuges, and cartridge
filters, which are used in industrial wastewater treatG&nt.
9.2.1 Limiting Technology: Filtration of Liquids
Filtration is a well developed process and most of the problems with
this process seata to be associated with the filter operation. The Bajor
problem with filter operation is maintaining the filter bed In good condition.
Inadequate cleaning results in s thin layer of compressible dirt or flue
around each grain of the med.'.ua. As the pressure drop across the filter
medium increases during the subsequent filter run, the grains are squeezed
together and cracks form in the surface of Che medium (Weber, 1972). These
dirty grains become larger In size gradually and sink to the bottom of the
9.4
-------
filter, reducing the filtration effectiveness.
9.2.2 Recycle, Reuse, Recovery Applications: Filtration of Liquids
Filtration ht-s been used for treatment of innumerable types of industrial
wastewaters. Multimedia filtration is commonly used for removal of the
metal precipitates from wasteuater after it has been subjected to precipita-
tion, fl-eculation, and sedimentation. Filtration is also used for dewater-
ing of waste sludges from biological treatment systems.
9.3 FILTRATION OF GASES
Filtration is the oldest method used for removal of suspended aaterials
In gases. It operates on the principle of passing dust-laden gases through
porous filter media in which the dust is trapped. Filtration methods form
one of the largest families of gas cleaning devices, and can be applied over
a wide range of conditions.
All filter media collect dust by a combination of effect susamrized
below:
1. Particles larger than the pore sise of the msdiuas will be separated
due to a sieving effect of the tasdiuta.
i
2. Particles may be separated by an inertial effect created by the
many changes of direction the particle smist undergo in passage through a
tortuous filter medium.
3. Fine dust particlejs aay be deposited on the filter mediusa as a
result of the electrostatic charge which they often carry.
A. Sub-s'tcron size particles having a weight similar to that of the
molecules of carrier gas will not be separated by inertial effects. They
will instead be subject to Brownian movement, and as a result will be brought
into close proximity to the filter medium, where they are deposited and held
9.5
-------
by electrostatic and molecular forces.
5. Particles smaller than the filter pores will be efficiently retain-
ed by a layer of dust which accumulates on and within the filter material.
This layer will create a pressure drop ac.-oss the filter which must be taken
into account during plant design.
Filter media can be broadly considered under three; headings:
1. Gravel or Sand Aggregate Bed
2. Porous Paper and Fibrous Mats
3. Woven and Felted Fabric Filters
Aggregate bed filters consist of uniform size particles such as sand or
gravel. These filters are not currently in wide use for industrial gas
cleaning. Gas cleaning efficiency increases with decreasing size of aggregate
and with increasing depth of bed. In one application, beds of fine sand two
meters deep were used to filter particles of radioactive material from exhaust
gases. These filters were found to be over 99 percent effective even on sub-
micron particles.
The aggregate filter is simple in design and can be used at elevated
temperatures. When such filters are used on gases with high moisture con-
tent, it is necessary to keep the aggregate above deupoint when dust-laden
gases are introduced. This prevents blockage of the bed by wet dust which is
not dislodged by normal cleaning methods.
Fluidized beds of aggregate have generally been found to be somewhat low
in efficiency (approximately 80 percent) due to re-entrsioasent of dust caused
by notion of the bed.
Paper filters, due to their relatively poor mechanical properties, are
normally used at lover temperatures where dust concentrations ara less than
5 mg-sf^. These filters are not normally used for industrial pollution
control requirements.
9.6
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Fibrous mat filters consist of fibers of a natural, synthetic, or glass
nature. The fibers may be mounted in mat form between supporting sheets of
gause or perforated metal. Filter characteristics vary according to depth of
filter, material of construction, and the density of filter packing. Fibrous
filters remove coarser material, but when pressure losses rise to 15-30 cm
W.G. due to packing density, high collection efficiencies are possible for
materials as fine as the sub-micron acid mist originating from sulphuric acid
plants.
Because of the many different kinds of filter material available, fibrous
filters are useful over a wide range of operating variables such as tempera-
ture and corrosivity. Their application is limited, hcvever, to streams
containing relatively low concentrations of dust- When resistance rises to
an unacceptable level, they must be cleaned or replaced.
Fabric filters take the form of woven fabric or felted taaterials manu-
factured from natural or man-made fibers. They are capable of treating large
gas volumes with high dust concentrations on a continuous basis. The design
filter rate is usually in the range of a pressure logs of 6-12 cm W.G.,
depending on whether the cloth is clean or has a layer of dust deposited on
it.
Woven cloth has relatively large gaps where its threads cross, vfhich may
also be large in comparison with the particles to be caught. This will
result in low efficiency with new filter bags, but as the dust builds up and
blocks the holes, efficiency improves. Eventually, filtration efficiency is
determined not by the filter, but by the dust layer, alloying particles below
1 meter to be caught.
Felted cloth avoids the problem of regular holess since its fibers are
9.7
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laid in random fashion. The pile on its surface also increases effective
filtering area, although this pile makes effective cleaning more difficult.
Synthetic fibers, lack natural felcing properties, and must undergo a process
in which a felt ia artificially induced by passing barbed needles through Che
fiber mat:. It has been reported that needle fibers combine the high filter
rate of felts with th filtered dust will become caked on the fibers,
eventually rtauliing ia blinding of the media.
Removal of dust from baric filters is accomplished by flexing or collaps-
ing the bag and blowing the 'sccuaulaced dust fron its surface.
Corrosive elements of gas and dust, as well as sharp edges on the dust
particles, can result in rapid failure of the filter. Preferably, filter
1
material shoald be chosen which has a life of several years. Another opera-
tional problem may arise when explosive mixtures are filtered due to the
electrical insulating properties of natural and synthetic fibers. If the
electrostatic charge is allowed to build up, it creates an increase in
voltage which may cause arcing through the gas. Explosion or fire may
result. This problem can be avoided by introducing a small quantity of
9.8
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conducting fiber such as metal into Che cloth in order to give it anti-static
properties.
Efficiency for fabric filters is always high (Parker, 1978). Collection
efficiencies in excess o£ 99.5 percent are normal. Fabric filters ere comraon-
7 n
ly used for control of dust concentrations in the range of 10 "Mg/ra (urban
3 3
atmospheric dust) to 10 yg/m (pneumatic conveying). They provide effective
removal of particles ranging in size from submicrometer fumes to 200um
powders (Billings, 1977).
9.3.1 Limiting Technology
Filter media used for removal of suspended naterials in gases can be
broadly grouped into three categories: gravel or sand aggregate beds; porous
paper and fibrous mats; and woven and felted fabric filters.
The aggregate filter is simple in design and can be used on dust-laden
gases with high moisture content, it is necessary to keep the aggregate above
dewpoir.t to prevent blockage of the bed by wet dust which is not dislodged by
normal cleaning methods. Fluidized aggregate beds may have low efficiency
due to re-eRtraimnent of dust caused by motion of the bed.
Paper filters have poor raechsnical propertiesB and are not normally used
for industrial pollution control.
Fibrous filters are useful over a wide range of operating conditions
such as temperature end corrosivity due to Che many types of filter material
available. Their application Is limited to streams containing relatively low
dust concentrations.
Fabric filters are capable of treating large gas volumes with high dust
concentration on a continuous basis. With woven cloth filters having large
holes filtration efficiency is determined ultimately by the dust layer vhich
9.9
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collects on the filter, and not by the filter itself. The use of felted
cloth eliminates the problem of regular holes, since its fibers are laid in
random fashion.
The temperature range for the use of fabric filters is restricted by the
type of filter material. New materials are being tested which are expected
to extend the range of operating temperatures to 400° C and above. The g&s
temperature must stay above dewpoint to eliminate the problem of dust caking
on the filters.
Corrosive elements of gas and dust and sharp dust particles edges can
cause rapid filter failure. An additional operational problem is the build-
ing up of electrostatic charge on the filter. This must be prevented in
order to prevent explosion of gas or an outbreak of fire. Introduction of a
small quantity of conducting fiber into the filter cloth will give it anti-
static properties.
Collection efficiencies in excess of 99.5 percent are normal for fabric
filters.
9.3.2 Recycle, Recovery, and Reuse Applications: Orgaaics
Due to the shortage of oil, the recycling of asphaltic pavement became
an issue of interest. A problem which occurs in trying to convert conven-
tional asphalt plants to plants which have recycle capabilities is the forma-
tion of fine particulete smoke which occurs whtn crushed pavement is subject-
ed to temperatures necessary for recycling. At these temperatures, the
asphalt begins to crack and release hydrocarbon vapor which condenses into
submicron droplets. These oily droplets are poorly collected by baghouse
filters and venturi scrubbers, devices currently in use at asphalt plants.
The electrofluidised bed (EFB), designed for high efficiency collection
9.10
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of submicron particles, was tested on emissions from an asphalt recycling
plant. The hydrocarbon pollutant is collected on sand which is then removed
from the bed in its fluidized state and added to the asphalt product.
Efficiencies of collection in excess of 98 percent were reported for submicrcTr-
particles in beds having unfluidized depths of 8-12 cm, using sand having a
mean diameter of 2 mm. Using this procedure, it was possible to combine
collection of submicron particles at high efficiency with the recycling and
reuse of the collected hydrocarbons and the filter sand (Zieve, et al.
1978).
9.3.3 Recycle, Recovery, and Reuse Applications: Inorganics
In certain manufacturing operations involving expensive water insoluble
dusts or powders in which excess material is norraally exhausted as part of
the operation, it has been found to be economical to collect exhaust material
in a filter from which t:he retained materials can be recovered. Such a
method is used for collecting phosphor particles produced in-forming color
cathode rav tubes by the dry phosphor technique.
Excess phosphor particles are collected from the exhaust atmosphere by
passing exhaust air through several filter media. The first filter is normal-
ly coarse woven, and is cleaned by vacuuming, shakings or beating. The
remaining superfines are then collected by filters made of materials such as
cellulose, glass, or plastic in the forra of fibrous compactions. These
filters are not suited to mechanical removal of phosphor without destruction.
In some cases, the phosphor particles have been dissolved for reclamation by
organic solvents or similar chemicals. This is an expensive process, however,
and caustic solvents may be detrimental to the phosphor (Warner, 1971).
Warner (1971) developed a decomposable filter for collecting water in
9.11
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soluble particles of gasborne materials. The filter medium is comprised of
water soluble organics which are stable in an environment have ambient rela-
tive humidity less than 90 percent and an ambient temperature under 100°C.
Particluate material is reclaimed by dissolving the filter in water. The
particulate matter la allowed to settle, and is recovered by decanting the
supernatant. Alternatively, the mixture of particulate and dissolved filter
medium is passed through a recirculating filter having a core of perforated
discs upon which the particulates are collected. Heated air is then forced
through the filter in a reverse manner to dislodge and dry the collected
particulate.
9.4 FLOTATION
Flotation is a unit operation used to separate solid or liquid particles
from a liquid phase. Separation IB brought cbout by introducing fine air
bubbles into the liquid phase. The bubbles attach to the particulate matter
and the buoyant force of the combined particle and gas bubbles is large
enough to cause the particle to rise to the surface (Metcalf and EddyB I9SO).
Three methods of introducing gas bubbles have been shown to create bubbles
sufficiently fine for flotation of suspended solids in municipal and indus-
trial wastewaters.
1) Injection of air while the liquid is under pressure, followed
by release of the pressure (dissolved air flotation).
2) Aeration at atmospheric pressure through revolving impeller or
porous media.
3) Application of a vacuum to the wastewatert which is saturated with
air at atmospheric pressure.
In biological treatment systems, biological flotation occurs when the
9.12
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gases formed by natural biological activity attached to the suspended solids
and rise upwards through the liquid. For any of those systems, the degree of
removal can be enhanced through the use of various chemical additives (Metcalf
and Eddy, 1980).
9.A.I Dissolved Air Flotation
In dissolved air flotation (DAF) systems, bubbles of size lOOp or less
are obtained by dissolving air in water ac an elevated pressure and then
reducing the pressure of the air-water mixture. The water if. pressurized in
the range of 40-80 psi and a stream of air is injected into the pressurized
water and retained in a tank under pressure for several mir.iites to allow tine
for the air to dissolve. At 60 F, about one cubic font of air is used for
each 100 gallons of air-charged water (U.S. EPA, Jan. 1975). The air-charged
water then passes through a pressure reducing valve into the flotation
?
i
treatment tank. The reduction in pressure causes the solubility of the air
to decrease and excess air cotaes out of solution in the fona of minute bubbles
(average size ISp). These bubbles attach to the sludge particles and increase
their bouyancy, causing them to float to '.he surface. In some capes a portion
of the effluent (15-120 per cent) is recycled, pressurized end seal-saturated
with air (Ketcalf and ^iddy, 1980).
I
A coagulant aid may be used with a DAF unit in order Co 1) increase the
allowable solids loading; 2) increase the percentage of floated solids; and
3) improve the clarity of the subnatant.
9.4.2 Air Flotation
In air-flotation systems, air bubbles are formed in the flotation tank
by a revolving impeller or through diffusers. These systems are not common
in Industrial wastewater treatment operations.
9.13
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9.4.3 Vacuum Flotation
In vacuum flotation systems, the vastewater is initially saturated
with air and a partial vacuum is then applied which causes the dissolved
air to come out of solution as minute bubbles. These bubbles attached to the
sludge particles in wastewater and rise to the surface to form a scura blanket,
which is easily removed by a skimming mechanism.
9.4.4 Recycle, Recovery and Reuse Applications
Flotation is a process of ore concentration developed and osed princi-
pally by the mineral industry. In uastevater treatment it is mostly used to
remove suspended matter and concentrate biological sludges. There have been
a number of other applications of flotation in the waste treatment area.
In a variation of the process called precipitate flotation, precipitates
can be collected en the top of the flotation tenk and recovered as a froth
concentrate (Arthur D. Little, Inc., 1975). In tltls application, the natal
to be removed from solution is precipitated. Another possible application
of precipitate flotation is the flotation of complexed cyanide (for example,
ferrocyanide precipitate) as a means of reraoving cyanide frcsa solutions
(Grieves and Bhattscharya, 1969).
In another variation of ths flotation process, known as ion-flotation,
a surfactant ion of opposite charge to the inorganic ion removed from solu-
tion is added in stoichiometric amounts. The surfactant, which must exist
in solution as simple ions, reacts with the inorganic ion to form an insoluble
"soap" which is raised to the surface with a bubbling action. Rubin e_t al.
(1966) reported removal o± dissolved copper with sodium lauryl sulfate using
the ion flotation process.
The insoluble metal precipitates formed during ion and precipitate
9.14
-------
flotation processes can be further subjected to treatment for recovery of
metals.
The flotation process la used for recovery of copper from the slag
generated in smeltcra (Matheson, ejt &l_. 1976). Flotation is also used for
removal of oil from industrial wastewarers such as those from refineries.
9.5 LIQUID-LIQUID EXTRACTION
Liquid-Liquid extraction has becoae an important separation technique
used by various industries either to remove small amounts of an impurity fros
a product stream or to separate products. This technique Is considered to be
a viable waste treatment process for selected waste streams, where recovery
of material is possible. The major applications of this process in vaste-
water treatment engineering are 1) recovery of phenol and related compounds
frosi wastewatjrs and 2) removal of water soluble solvents such aa alcohol
from wastes containing raixed chlorinated hydrocarbon solvents.
Liquid-Liquid extraction, hereinafter referred to as solvent eictractioa,
involves separating the components of a liquid mixture by the addition of
another liquid referred to as the solvent which is itsmiacible or only parti-
ally raisclble) with the initial phase. The solvent is chosen such that one
of more of the components of the original solution, called the solute.
will transfer preferentially into th*; solvent phase, leaving the others
behind in the ao-called "faffinate." The product of the desired solute in
the solvent is called the extract. At equilibrium, the ratio of the coacen-
I
trations of solute in the extract, y, and raffinate, x, phases is called the
distribution coefficient D. The coefficient ie used as an indicator of the
ability of a solvent to extract a particular solute.
The proportion of solute recovery in a single equilibration depends on
9.15
-------
both the distribution coefficients for that solute and the relative amount of.
solvent used. To obtain a high recovery without using an excessive amount of
solvent (with the corresponding production of a very dilute extract), most
processes employ multistage countercurrent contacting (Hanson, 1979).
The purity of the initial extract Is oftsn enhanced by scrubbing with a
suitable immiscible phase such that bulk of the desired solute in the solvenr
phase is retained while the impurities are washed out. The scrub feed is
usually based on the same solvent as the original feed and the scrub raffi-
nate is then combined with the nairi feed to permit recovery of any of the
desired solute which may have transferred.
The solute may be removed from the extracted solvent by a second solvent
extraction step, distillation, or an alternative process. Depending upon
cost considerations, solvent recovery from the treated streoa Ray be advan-
tageous. This may be accomplished by stripping, distillation, adsorption, ca
)
other suitable process, A typical slngle-Btege solvent extraction process is
illustrated in Figure 6.1.
Various devices we're developed through the years to establish phase
equilibrium rapidly and thereby accomplish solvent extraction based on a
combination of capital and operating costs. Several discussions (Oberg and
i
Jones, 1963; Bailes, e$al. 1976; Reissinger and Schroeter, 1978a, 1978b) on
the various extraction devices in use ere available in the literature.
The extraction devices have two things In coiamoa; first, they generate a
large amount of interfacial area between the two liquid phases mostly by dis-
persing one phase in the other and second, they impart mechanical energy into
the system by means of agitation to maintain a degree of turbulence in one or
both phases (Eckert, 1976). An overall review of industrial extractors and
9.16
-------
their relationship co different extraction processes IE given in Figure 6.2.
A thorough discussion of the different types of extractions in Figure 6.2 is
given by Reissiriaer and Schroetcr (]978a, 197Gb).
There is no general guide to contactor selection. Most of the contactors
available In the market asy be used for simple processes and a final choice
vill depend on the results of an economic evaluation of available options as
well as the consideration of local factors such as space availability (Bailes,
et^ a^. 1976). Reiesinger and Schroeter (1978a, 1978b)n have attempted to
establish a selection procedure based on the use of a diagram into which the
most isportant parameters have been incorporated. The suggested scheme -say
only be used as a rule of thumb, however. The final design of a specific
solvent extraction unit of a new application should be preceded by detail&d
laboratory tests as well as technical and econaaic coraparisosis with competing
processes.
9.5.1 Limiting Technology
Liquid-liquid (solvent) extraction is a well established process which
have relatively few insurmountable technical problems. The problems associ-
ated with the epplieation of solvent extraction Eo recovery of by-products
from waste streams are basically related to the difficulty in selecting
solvents and a contactor, which are, in combination, capable of producing the
desired results.
9.5.2 Recycle, Recovery and Reuse Applications
Liquid-Liquid extraction is being used in both conm«rcial processing and
wash applications. The following are the tasjor waste treatment applications:
1) Removal and recovery of phenol and related compounds from petroleum
•refinery waste (Anonymous, 1973; Coke-oven liquors, Carbone, 1967;
9.17
-------
Aver et_ a^. 1969) and phenol resin plant effluents (Wunn, 1963).
2) Removal and recovery of water-soluble solvents such as alcohoJ frora
wastes containing chlorinated hydrocarbon solvents.
3) Extraction of thiazole-based chemicals (Anonymous, 1970), acetic
acid (Hinraelsfcein, 1974) and Salicylic acid (Anonymous, 1970).
9.18
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i
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